OCL Constraints

OCL Constraints and Validation

Learn to define and validate OCL constraints on Ecore models.

The Object Constraint Language (OCL) allows you to specify invariants, derivation rules, and pre/post conditions that models must satisfy. In this tutorial, you’ll:

Define invariant constraints on model elements
Use collection operations for validation
Create derived attributes with OCL expressions
Validate models against constraints

40 mins Estimated Time

Section 1

Understanding OCL Constraints

OCL constraints specify rules that model instances must follow. They’re expressed as boolean expressions that evaluate to true for valid models.

Types of OCL constraints:

Invariants: Conditions that must always be true
Derivation rules: How to compute derived attributes
Pre/post conditions: Method contracts (input/output)

Common OCL operations:

forAll: All elements satisfy condition
exists: At least one element satisfies condition
select/reject: Filter collections
isUnique: All values are distinct
size: Collection element count

Step 1

Examine the Bank Account metamodel with OCL constraints ensuring unique account numbers, valid emails, adult customers, positive balances, and proper account formats.

bank-account.ecore

1<?xml version="1.0" encoding="UTF-8"?>
2<ecore:EPackage xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="Bank" nsURI="http://www.example.org/bank" nsPrefix="bank">
4
5  <!-- OCL Constraints Documentation -->
6  <eAnnotations source="http://www.eclipse.org/emf/2002/GenModel">
7    <details key="documentation" value="Bank Account metamodel demonstrating OCL constraints including invariants, derivation rules, and pre/post conditions."/>
8  </eAnnotations>
9
10  <!-- Bank: Container for customers and accounts -->
11  <eClassifiers xsi:type="ecore:EClass" name="Bank">
12    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
13      <details key="constraints" value="uniqueAccountNumbers uniqueCustomerIds"/>
14    </eAnnotations>
15    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
16      <!-- Invariant: All account numbers must be unique -->
17      <details key="uniqueAccountNumbers" value="self.accounts->isUnique(accountNumber)"/>
18      <!-- Invariant: All customer IDs must be unique -->
19      <details key="uniqueCustomerIds" value="self.customers->isUnique(customerId)"/>
20    </eAnnotations>
21    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
22        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
23    <eStructuralFeatures xsi:type="ecore:EAttribute" name="swiftCode" lowerBound="1"
24        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
25    <eStructuralFeatures xsi:type="ecore:EReference" name="customers" upperBound="-1"
26        eType="#//Customer" containment="true" eOpposite="#//Customer/bank"/>
27    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
28        eType="#//Account" containment="true" eOpposite="#//Account/bank"/>
29  </eClassifiers>
30
31  <!-- Customer: Bank customer with accounts -->
32  <eClassifiers xsi:type="ecore:EClass" name="Customer">
33    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
34      <details key="constraints" value="validEmail adultCustomer"/>
35    </eAnnotations>
36    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
37      <!-- Invariant: Email must contain @ symbol -->
38      <details key="validEmail" value="self.email.indexOf('@') > 0"/>
39      <!-- Invariant: Customer must be at least 18 years old -->
40      <details key="adultCustomer" value="self.age >= 18"/>
41    </eAnnotations>
42    <eStructuralFeatures xsi:type="ecore:EAttribute" name="customerId" lowerBound="1"
43        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
44    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
45        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
46    <eStructuralFeatures xsi:type="ecore:EAttribute" name="email" lowerBound="1"
47        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
48    <eStructuralFeatures xsi:type="ecore:EAttribute" name="age" lowerBound="1"
49        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"/>
50    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
51        eOpposite="#//Bank/customers"/>
52    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
53        eType="#//Account" eOpposite="#//Account/owner"/>
54    <!-- Derived: Total balance across all accounts -->
55    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalBalance" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
56        changeable="false" volatile="true" transient="true" derived="true">
57      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
58        <details key="derivation" value="self.accounts->collect(balance)->sum()"/>
59      </eAnnotations>
60    </eStructuralFeatures>
61    <!-- Derived: Number of active accounts -->
62    <eStructuralFeatures xsi:type="ecore:EAttribute" name="activeAccountCount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"
63        changeable="false" volatile="true" transient="true" derived="true">
64      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
65        <details key="derivation" value="self.accounts->select(isActive)->size()"/>
66      </eAnnotations>
67    </eStructuralFeatures>
68  </eClassifiers>
69
70  <!-- AccountType: Enum for account types -->
71  <eClassifiers xsi:type="ecore:EEnum" name="AccountType">
72    <eLiterals name="SAVINGS" value="0"/>
73    <eLiterals name="CURRENT" value="1"/>
74    <eLiterals name="FIXED_DEPOSIT" value="2"/>
75  </eClassifiers>
76
77  <!-- Account: Bank account with balance constraints -->
78  <eClassifiers xsi:type="ecore:EClass" name="Account">
79    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
80      <details key="constraints" value="positiveBalance validAccountNumber sufficientMinimumBalance"/>
81    </eAnnotations>
82    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
83      <!-- Invariant: Balance must not be negative -->
84      <details key="positiveBalance" value="self.balance >= 0"/>
85      <!-- Invariant: Account number must be 10 digits -->
86      <details key="validAccountNumber" value="self.accountNumber.size() = 10"/>
87      <!-- Invariant: Savings accounts must maintain minimum balance -->
88      <details key="sufficientMinimumBalance" value="self.accountType = AccountType::SAVINGS implies self.balance >= self.minimumBalance"/>
89    </eAnnotations>
90    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountNumber" lowerBound="1"
91        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
92    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountType" lowerBound="1"
93        eType="#//AccountType" defaultValueLiteral="SAVINGS"/>
94    <eStructuralFeatures xsi:type="ecore:EAttribute" name="balance" lowerBound="1"
95        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="0.0"/>
96    <eStructuralFeatures xsi:type="ecore:EAttribute" name="minimumBalance"
97        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="100.0"/>
98    <eStructuralFeatures xsi:type="ecore:EAttribute" name="isActive"
99        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean" defaultValueLiteral="true"/>
100    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
101        eOpposite="#//Bank/accounts"/>
102    <eStructuralFeatures xsi:type="ecore:EReference" name="owner" lowerBound="1" eType="#//Customer"
103        eOpposite="#//Customer/accounts"/>
104    <eStructuralFeatures xsi:type="ecore:EReference" name="transactions" upperBound="-1"
105        eType="#//Transaction" containment="true" eOpposite="#//Transaction/account"/>
106    <!-- Derived: Total deposits -->
107    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalDeposits" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
108        changeable="false" volatile="true" transient="true" derived="true">
109      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
110        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::DEPOSIT)->collect(amount)->sum()"/>
111      </eAnnotations>
112    </eStructuralFeatures>
113    <!-- Derived: Total withdrawals -->
114    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalWithdrawals" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
115        changeable="false" volatile="true" transient="true" derived="true">
116      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
117        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::WITHDRAWAL)->collect(amount)->sum()"/>
118      </eAnnotations>
119    </eStructuralFeatures>
120    <!-- Operation with pre/post conditions -->
121    <eOperations name="withdraw" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean">
122      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
123        <!-- Precondition: Amount must be positive -->
124        <details key="pre" value="amount > 0"/>
125        <!-- Precondition: Must have sufficient funds -->
126        <details key="pre" value="self.balance >= amount"/>
127        <!-- Postcondition: Balance is reduced -->
128        <details key="post" value="self.balance = self.balance@pre - amount"/>
129      </eAnnotations>
130      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
131    </eOperations>
132    <eOperations name="deposit">
133      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
134        <!-- Precondition: Amount must be positive -->
135        <details key="pre" value="amount > 0"/>
136        <!-- Postcondition: Balance is increased -->
137        <details key="post" value="self.balance = self.balance@pre + amount"/>
138      </eAnnotations>
139      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
140    </eOperations>
141  </eClassifiers>
142
143  <!-- TransactionType: Enum for transaction types -->
144  <eClassifiers xsi:type="ecore:EEnum" name="TransactionType">
145    <eLiterals name="DEPOSIT" value="0"/>
146    <eLiterals name="WITHDRAWAL" value="1"/>
147    <eLiterals name="TRANSFER" value="2"/>
148  </eClassifiers>
149
150  <!-- Transaction: Individual transaction record -->
151  <eClassifiers xsi:type="ecore:EClass" name="Transaction">
152    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
153      <details key="constraints" value="positiveAmount validDescription"/>
154    </eAnnotations>
155    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
156      <!-- Invariant: Transaction amount must be positive -->
157      <details key="positiveAmount" value="self.amount > 0"/>
158      <!-- Invariant: Description must not be empty -->
159      <details key="validDescription" value="self.description.size() > 0"/>
160    </eAnnotations>
161    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionId" lowerBound="1"
162        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
163    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionType" lowerBound="1"
164        eType="#//TransactionType"/>
165    <eStructuralFeatures xsi:type="ecore:EAttribute" name="amount" lowerBound="1"
166        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
167    <eStructuralFeatures xsi:type="ecore:EAttribute" name="description" lowerBound="1"
168        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
169    <eStructuralFeatures xsi:type="ecore:EAttribute" name="timestamp" lowerBound="1"
170        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
171    <eStructuralFeatures xsi:type="ecore:EReference" name="account" lowerBound="1" eType="#//Account"
172        eOpposite="#//Account/transactions"/>
173  </eClassifiers>
174</ecore:EPackage>

Section 2

Constraint Categories

Let’s examine the different types of constraints in detail. Each serves a specific validation purpose.

Step 1

Uniqueness constraints ensure no duplicate identifiers.

The uniqueAccountNumbers constraint uses isUnique() to verify all account numbers are distinct across the bank. Similarly, uniqueCustomerIds ensures customer IDs don’t repeat.

bank-account.ecore

1<?xml version="1.0" encoding="UTF-8"?>
2<ecore:EPackage xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="Bank" nsURI="http://www.example.org/bank" nsPrefix="bank">
4
5  <!-- OCL Constraints Documentation -->
6  <eAnnotations source="http://www.eclipse.org/emf/2002/GenModel">
7    <details key="documentation" value="Bank Account metamodel demonstrating OCL constraints including invariants, derivation rules, and pre/post conditions."/>
8  </eAnnotations>
9
10  <!-- Bank: Container for customers and accounts -->
11  <eClassifiers xsi:type="ecore:EClass" name="Bank">
12    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
13      <details key="constraints" value="uniqueAccountNumbers uniqueCustomerIds"/>
14    </eAnnotations>
15    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
16      <!-- Invariant: All account numbers must be unique -->
17      <details key="uniqueAccountNumbers" value="self.accounts->isUnique(accountNumber)"/>
18      <!-- Invariant: All customer IDs must be unique -->
19      <details key="uniqueCustomerIds" value="self.customers->isUnique(customerId)"/>
20    </eAnnotations>
21    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
22        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
23    <eStructuralFeatures xsi:type="ecore:EAttribute" name="swiftCode" lowerBound="1"
24        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
25    <eStructuralFeatures xsi:type="ecore:EReference" name="customers" upperBound="-1"
26        eType="#//Customer" containment="true" eOpposite="#//Customer/bank"/>
27    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
28        eType="#//Account" containment="true" eOpposite="#//Account/bank"/>
29  </eClassifiers>
30
31  <!-- Customer: Bank customer with accounts -->
32  <eClassifiers xsi:type="ecore:EClass" name="Customer">
33    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
34      <details key="constraints" value="validEmail adultCustomer"/>
35    </eAnnotations>
36    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
37      <!-- Invariant: Email must contain @ symbol -->
38      <details key="validEmail" value="self.email.indexOf('@') > 0"/>
39      <!-- Invariant: Customer must be at least 18 years old -->
40      <details key="adultCustomer" value="self.age >= 18"/>
41    </eAnnotations>
42    <eStructuralFeatures xsi:type="ecore:EAttribute" name="customerId" lowerBound="1"
43        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
44    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
45        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
46    <eStructuralFeatures xsi:type="ecore:EAttribute" name="email" lowerBound="1"
47        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
48    <eStructuralFeatures xsi:type="ecore:EAttribute" name="age" lowerBound="1"
49        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"/>
50    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
51        eOpposite="#//Bank/customers"/>
52    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
53        eType="#//Account" eOpposite="#//Account/owner"/>
54    <!-- Derived: Total balance across all accounts -->
55    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalBalance" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
56        changeable="false" volatile="true" transient="true" derived="true">
57      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
58        <details key="derivation" value="self.accounts->collect(balance)->sum()"/>
59      </eAnnotations>
60    </eStructuralFeatures>
61    <!-- Derived: Number of active accounts -->
62    <eStructuralFeatures xsi:type="ecore:EAttribute" name="activeAccountCount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"
63        changeable="false" volatile="true" transient="true" derived="true">
64      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
65        <details key="derivation" value="self.accounts->select(isActive)->size()"/>
66      </eAnnotations>
67    </eStructuralFeatures>
68  </eClassifiers>
69
70  <!-- AccountType: Enum for account types -->
71  <eClassifiers xsi:type="ecore:EEnum" name="AccountType">
72    <eLiterals name="SAVINGS" value="0"/>
73    <eLiterals name="CURRENT" value="1"/>
74    <eLiterals name="FIXED_DEPOSIT" value="2"/>
75  </eClassifiers>
76
77  <!-- Account: Bank account with balance constraints -->
78  <eClassifiers xsi:type="ecore:EClass" name="Account">
79    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
80      <details key="constraints" value="positiveBalance validAccountNumber sufficientMinimumBalance"/>
81    </eAnnotations>
82    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
83      <!-- Invariant: Balance must not be negative -->
84      <details key="positiveBalance" value="self.balance >= 0"/>
85      <!-- Invariant: Account number must be 10 digits -->
86      <details key="validAccountNumber" value="self.accountNumber.size() = 10"/>
87      <!-- Invariant: Savings accounts must maintain minimum balance -->
88      <details key="sufficientMinimumBalance" value="self.accountType = AccountType::SAVINGS implies self.balance >= self.minimumBalance"/>
89    </eAnnotations>
90    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountNumber" lowerBound="1"
91        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
92    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountType" lowerBound="1"
93        eType="#//AccountType" defaultValueLiteral="SAVINGS"/>
94    <eStructuralFeatures xsi:type="ecore:EAttribute" name="balance" lowerBound="1"
95        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="0.0"/>
96    <eStructuralFeatures xsi:type="ecore:EAttribute" name="minimumBalance"
97        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="100.0"/>
98    <eStructuralFeatures xsi:type="ecore:EAttribute" name="isActive"
99        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean" defaultValueLiteral="true"/>
100    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
101        eOpposite="#//Bank/accounts"/>
102    <eStructuralFeatures xsi:type="ecore:EReference" name="owner" lowerBound="1" eType="#//Customer"
103        eOpposite="#//Customer/accounts"/>
104    <eStructuralFeatures xsi:type="ecore:EReference" name="transactions" upperBound="-1"
105        eType="#//Transaction" containment="true" eOpposite="#//Transaction/account"/>
106    <!-- Derived: Total deposits -->
107    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalDeposits" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
108        changeable="false" volatile="true" transient="true" derived="true">
109      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
110        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::DEPOSIT)->collect(amount)->sum()"/>
111      </eAnnotations>
112    </eStructuralFeatures>
113    <!-- Derived: Total withdrawals -->
114    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalWithdrawals" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
115        changeable="false" volatile="true" transient="true" derived="true">
116      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
117        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::WITHDRAWAL)->collect(amount)->sum()"/>
118      </eAnnotations>
119    </eStructuralFeatures>
120    <!-- Operation with pre/post conditions -->
121    <eOperations name="withdraw" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean">
122      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
123        <!-- Precondition: Amount must be positive -->
124        <details key="pre" value="amount > 0"/>
125        <!-- Precondition: Must have sufficient funds -->
126        <details key="pre" value="self.balance >= amount"/>
127        <!-- Postcondition: Balance is reduced -->
128        <details key="post" value="self.balance = self.balance@pre - amount"/>
129      </eAnnotations>
130      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
131    </eOperations>
132    <eOperations name="deposit">
133      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
134        <!-- Precondition: Amount must be positive -->
135        <details key="pre" value="amount > 0"/>
136        <!-- Postcondition: Balance is increased -->
137        <details key="post" value="self.balance = self.balance@pre + amount"/>
138      </eAnnotations>
139      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
140    </eOperations>
141  </eClassifiers>
142
143  <!-- TransactionType: Enum for transaction types -->
144  <eClassifiers xsi:type="ecore:EEnum" name="TransactionType">
145    <eLiterals name="DEPOSIT" value="0"/>
146    <eLiterals name="WITHDRAWAL" value="1"/>
147    <eLiterals name="TRANSFER" value="2"/>
148  </eClassifiers>
149
150  <!-- Transaction: Individual transaction record -->
151  <eClassifiers xsi:type="ecore:EClass" name="Transaction">
152    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
153      <details key="constraints" value="positiveAmount validDescription"/>
154    </eAnnotations>
155    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
156      <!-- Invariant: Transaction amount must be positive -->
157      <details key="positiveAmount" value="self.amount > 0"/>
158      <!-- Invariant: Description must not be empty -->
159      <details key="validDescription" value="self.description.size() > 0"/>
160    </eAnnotations>
161    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionId" lowerBound="1"
162        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
163    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionType" lowerBound="1"
164        eType="#//TransactionType"/>
165    <eStructuralFeatures xsi:type="ecore:EAttribute" name="amount" lowerBound="1"
166        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
167    <eStructuralFeatures xsi:type="ecore:EAttribute" name="description" lowerBound="1"
168        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
169    <eStructuralFeatures xsi:type="ecore:EAttribute" name="timestamp" lowerBound="1"
170        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
171    <eStructuralFeatures xsi:type="ecore:EReference" name="account" lowerBound="1" eType="#//Account"
172        eOpposite="#//Account/transactions"/>
173  </eClassifiers>
174</ecore:EPackage>

Step 2

Format validation checks string patterns.

The validEmail constraint checks that email addresses contain an ‘@’ symbol. The validAccountNumber constraint verifies account numbers are exactly 10 digits.

bank-account.ecore

1<?xml version="1.0" encoding="UTF-8"?>
2<ecore:EPackage xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="Bank" nsURI="http://www.example.org/bank" nsPrefix="bank">
4
5  <!-- OCL Constraints Documentation -->
6  <eAnnotations source="http://www.eclipse.org/emf/2002/GenModel">
7    <details key="documentation" value="Bank Account metamodel demonstrating OCL constraints including invariants, derivation rules, and pre/post conditions."/>
8  </eAnnotations>
9
10  <!-- Bank: Container for customers and accounts -->
11  <eClassifiers xsi:type="ecore:EClass" name="Bank">
12    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
13      <details key="constraints" value="uniqueAccountNumbers uniqueCustomerIds"/>
14    </eAnnotations>
15    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
16      <!-- Invariant: All account numbers must be unique -->
17      <details key="uniqueAccountNumbers" value="self.accounts->isUnique(accountNumber)"/>
18      <!-- Invariant: All customer IDs must be unique -->
19      <details key="uniqueCustomerIds" value="self.customers->isUnique(customerId)"/>
20    </eAnnotations>
21    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
22        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
23    <eStructuralFeatures xsi:type="ecore:EAttribute" name="swiftCode" lowerBound="1"
24        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
25    <eStructuralFeatures xsi:type="ecore:EReference" name="customers" upperBound="-1"
26        eType="#//Customer" containment="true" eOpposite="#//Customer/bank"/>
27    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
28        eType="#//Account" containment="true" eOpposite="#//Account/bank"/>
29  </eClassifiers>
30
31  <!-- Customer: Bank customer with accounts -->
32  <eClassifiers xsi:type="ecore:EClass" name="Customer">
33    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
34      <details key="constraints" value="validEmail adultCustomer"/>
35    </eAnnotations>
36    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
37      <!-- Invariant: Email must contain @ symbol -->
38      <details key="validEmail" value="self.email.indexOf('@') > 0"/>
39      <!-- Invariant: Customer must be at least 18 years old -->
40      <details key="adultCustomer" value="self.age >= 18"/>
41    </eAnnotations>
42    <eStructuralFeatures xsi:type="ecore:EAttribute" name="customerId" lowerBound="1"
43        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
44    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
45        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
46    <eStructuralFeatures xsi:type="ecore:EAttribute" name="email" lowerBound="1"
47        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
48    <eStructuralFeatures xsi:type="ecore:EAttribute" name="age" lowerBound="1"
49        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"/>
50    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
51        eOpposite="#//Bank/customers"/>
52    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
53        eType="#//Account" eOpposite="#//Account/owner"/>
54    <!-- Derived: Total balance across all accounts -->
55    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalBalance" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
56        changeable="false" volatile="true" transient="true" derived="true">
57      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
58        <details key="derivation" value="self.accounts->collect(balance)->sum()"/>
59      </eAnnotations>
60    </eStructuralFeatures>
61    <!-- Derived: Number of active accounts -->
62    <eStructuralFeatures xsi:type="ecore:EAttribute" name="activeAccountCount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"
63        changeable="false" volatile="true" transient="true" derived="true">
64      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
65        <details key="derivation" value="self.accounts->select(isActive)->size()"/>
66      </eAnnotations>
67    </eStructuralFeatures>
68  </eClassifiers>
69
70  <!-- AccountType: Enum for account types -->
71  <eClassifiers xsi:type="ecore:EEnum" name="AccountType">
72    <eLiterals name="SAVINGS" value="0"/>
73    <eLiterals name="CURRENT" value="1"/>
74    <eLiterals name="FIXED_DEPOSIT" value="2"/>
75  </eClassifiers>
76
77  <!-- Account: Bank account with balance constraints -->
78  <eClassifiers xsi:type="ecore:EClass" name="Account">
79    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
80      <details key="constraints" value="positiveBalance validAccountNumber sufficientMinimumBalance"/>
81    </eAnnotations>
82    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
83      <!-- Invariant: Balance must not be negative -->
84      <details key="positiveBalance" value="self.balance >= 0"/>
85      <!-- Invariant: Account number must be 10 digits -->
86      <details key="validAccountNumber" value="self.accountNumber.size() = 10"/>
87      <!-- Invariant: Savings accounts must maintain minimum balance -->
88      <details key="sufficientMinimumBalance" value="self.accountType = AccountType::SAVINGS implies self.balance >= self.minimumBalance"/>
89    </eAnnotations>
90    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountNumber" lowerBound="1"
91        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
92    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountType" lowerBound="1"
93        eType="#//AccountType" defaultValueLiteral="SAVINGS"/>
94    <eStructuralFeatures xsi:type="ecore:EAttribute" name="balance" lowerBound="1"
95        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="0.0"/>
96    <eStructuralFeatures xsi:type="ecore:EAttribute" name="minimumBalance"
97        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="100.0"/>
98    <eStructuralFeatures xsi:type="ecore:EAttribute" name="isActive"
99        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean" defaultValueLiteral="true"/>
100    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
101        eOpposite="#//Bank/accounts"/>
102    <eStructuralFeatures xsi:type="ecore:EReference" name="owner" lowerBound="1" eType="#//Customer"
103        eOpposite="#//Customer/accounts"/>
104    <eStructuralFeatures xsi:type="ecore:EReference" name="transactions" upperBound="-1"
105        eType="#//Transaction" containment="true" eOpposite="#//Transaction/account"/>
106    <!-- Derived: Total deposits -->
107    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalDeposits" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
108        changeable="false" volatile="true" transient="true" derived="true">
109      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
110        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::DEPOSIT)->collect(amount)->sum()"/>
111      </eAnnotations>
112    </eStructuralFeatures>
113    <!-- Derived: Total withdrawals -->
114    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalWithdrawals" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
115        changeable="false" volatile="true" transient="true" derived="true">
116      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
117        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::WITHDRAWAL)->collect(amount)->sum()"/>
118      </eAnnotations>
119    </eStructuralFeatures>
120    <!-- Operation with pre/post conditions -->
121    <eOperations name="withdraw" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean">
122      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
123        <!-- Precondition: Amount must be positive -->
124        <details key="pre" value="amount > 0"/>
125        <!-- Precondition: Must have sufficient funds -->
126        <details key="pre" value="self.balance >= amount"/>
127        <!-- Postcondition: Balance is reduced -->
128        <details key="post" value="self.balance = self.balance@pre - amount"/>
129      </eAnnotations>
130      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
131    </eOperations>
132    <eOperations name="deposit">
133      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
134        <!-- Precondition: Amount must be positive -->
135        <details key="pre" value="amount > 0"/>
136        <!-- Postcondition: Balance is increased -->
137        <details key="post" value="self.balance = self.balance@pre + amount"/>
138      </eAnnotations>
139      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
140    </eOperations>
141  </eClassifiers>
142
143  <!-- TransactionType: Enum for transaction types -->
144  <eClassifiers xsi:type="ecore:EEnum" name="TransactionType">
145    <eLiterals name="DEPOSIT" value="0"/>
146    <eLiterals name="WITHDRAWAL" value="1"/>
147    <eLiterals name="TRANSFER" value="2"/>
148  </eClassifiers>
149
150  <!-- Transaction: Individual transaction record -->
151  <eClassifiers xsi:type="ecore:EClass" name="Transaction">
152    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
153      <details key="constraints" value="positiveAmount validDescription"/>
154    </eAnnotations>
155    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
156      <!-- Invariant: Transaction amount must be positive -->
157      <details key="positiveAmount" value="self.amount > 0"/>
158      <!-- Invariant: Description must not be empty -->
159      <details key="validDescription" value="self.description.size() > 0"/>
160    </eAnnotations>
161    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionId" lowerBound="1"
162        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
163    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionType" lowerBound="1"
164        eType="#//TransactionType"/>
165    <eStructuralFeatures xsi:type="ecore:EAttribute" name="amount" lowerBound="1"
166        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
167    <eStructuralFeatures xsi:type="ecore:EAttribute" name="description" lowerBound="1"
168        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
169    <eStructuralFeatures xsi:type="ecore:EAttribute" name="timestamp" lowerBound="1"
170        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
171    <eStructuralFeatures xsi:type="ecore:EReference" name="account" lowerBound="1" eType="#//Account"
172        eOpposite="#//Account/transactions"/>
173  </eClassifiers>
174</ecore:EPackage>

Step 3

Business rules encode domain logic.

The adultCustomer constraint requires customers to be at least 18 years old. The sufficientMinimumBalance constraint ensures savings accounts maintain their minimum balance.

bank-account.ecore

1<?xml version="1.0" encoding="UTF-8"?>
2<ecore:EPackage xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="Bank" nsURI="http://www.example.org/bank" nsPrefix="bank">
4
5  <!-- OCL Constraints Documentation -->
6  <eAnnotations source="http://www.eclipse.org/emf/2002/GenModel">
7    <details key="documentation" value="Bank Account metamodel demonstrating OCL constraints including invariants, derivation rules, and pre/post conditions."/>
8  </eAnnotations>
9
10  <!-- Bank: Container for customers and accounts -->
11  <eClassifiers xsi:type="ecore:EClass" name="Bank">
12    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
13      <details key="constraints" value="uniqueAccountNumbers uniqueCustomerIds"/>
14    </eAnnotations>
15    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
16      <!-- Invariant: All account numbers must be unique -->
17      <details key="uniqueAccountNumbers" value="self.accounts->isUnique(accountNumber)"/>
18      <!-- Invariant: All customer IDs must be unique -->
19      <details key="uniqueCustomerIds" value="self.customers->isUnique(customerId)"/>
20    </eAnnotations>
21    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
22        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
23    <eStructuralFeatures xsi:type="ecore:EAttribute" name="swiftCode" lowerBound="1"
24        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
25    <eStructuralFeatures xsi:type="ecore:EReference" name="customers" upperBound="-1"
26        eType="#//Customer" containment="true" eOpposite="#//Customer/bank"/>
27    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
28        eType="#//Account" containment="true" eOpposite="#//Account/bank"/>
29  </eClassifiers>
30
31  <!-- Customer: Bank customer with accounts -->
32  <eClassifiers xsi:type="ecore:EClass" name="Customer">
33    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
34      <details key="constraints" value="validEmail adultCustomer"/>
35    </eAnnotations>
36    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
37      <!-- Invariant: Email must contain @ symbol -->
38      <details key="validEmail" value="self.email.indexOf('@') > 0"/>
39      <!-- Invariant: Customer must be at least 18 years old -->
40      <details key="adultCustomer" value="self.age >= 18"/>
41    </eAnnotations>
42    <eStructuralFeatures xsi:type="ecore:EAttribute" name="customerId" lowerBound="1"
43        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
44    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
45        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
46    <eStructuralFeatures xsi:type="ecore:EAttribute" name="email" lowerBound="1"
47        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
48    <eStructuralFeatures xsi:type="ecore:EAttribute" name="age" lowerBound="1"
49        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"/>
50    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
51        eOpposite="#//Bank/customers"/>
52    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
53        eType="#//Account" eOpposite="#//Account/owner"/>
54    <!-- Derived: Total balance across all accounts -->
55    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalBalance" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
56        changeable="false" volatile="true" transient="true" derived="true">
57      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
58        <details key="derivation" value="self.accounts->collect(balance)->sum()"/>
59      </eAnnotations>
60    </eStructuralFeatures>
61    <!-- Derived: Number of active accounts -->
62    <eStructuralFeatures xsi:type="ecore:EAttribute" name="activeAccountCount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"
63        changeable="false" volatile="true" transient="true" derived="true">
64      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
65        <details key="derivation" value="self.accounts->select(isActive)->size()"/>
66      </eAnnotations>
67    </eStructuralFeatures>
68  </eClassifiers>
69
70  <!-- AccountType: Enum for account types -->
71  <eClassifiers xsi:type="ecore:EEnum" name="AccountType">
72    <eLiterals name="SAVINGS" value="0"/>
73    <eLiterals name="CURRENT" value="1"/>
74    <eLiterals name="FIXED_DEPOSIT" value="2"/>
75  </eClassifiers>
76
77  <!-- Account: Bank account with balance constraints -->
78  <eClassifiers xsi:type="ecore:EClass" name="Account">
79    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
80      <details key="constraints" value="positiveBalance validAccountNumber sufficientMinimumBalance"/>
81    </eAnnotations>
82    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
83      <!-- Invariant: Balance must not be negative -->
84      <details key="positiveBalance" value="self.balance >= 0"/>
85      <!-- Invariant: Account number must be 10 digits -->
86      <details key="validAccountNumber" value="self.accountNumber.size() = 10"/>
87      <!-- Invariant: Savings accounts must maintain minimum balance -->
88      <details key="sufficientMinimumBalance" value="self.accountType = AccountType::SAVINGS implies self.balance >= self.minimumBalance"/>
89    </eAnnotations>
90    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountNumber" lowerBound="1"
91        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
92    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountType" lowerBound="1"
93        eType="#//AccountType" defaultValueLiteral="SAVINGS"/>
94    <eStructuralFeatures xsi:type="ecore:EAttribute" name="balance" lowerBound="1"
95        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="0.0"/>
96    <eStructuralFeatures xsi:type="ecore:EAttribute" name="minimumBalance"
97        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="100.0"/>
98    <eStructuralFeatures xsi:type="ecore:EAttribute" name="isActive"
99        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean" defaultValueLiteral="true"/>
100    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
101        eOpposite="#//Bank/accounts"/>
102    <eStructuralFeatures xsi:type="ecore:EReference" name="owner" lowerBound="1" eType="#//Customer"
103        eOpposite="#//Customer/accounts"/>
104    <eStructuralFeatures xsi:type="ecore:EReference" name="transactions" upperBound="-1"
105        eType="#//Transaction" containment="true" eOpposite="#//Transaction/account"/>
106    <!-- Derived: Total deposits -->
107    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalDeposits" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
108        changeable="false" volatile="true" transient="true" derived="true">
109      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
110        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::DEPOSIT)->collect(amount)->sum()"/>
111      </eAnnotations>
112    </eStructuralFeatures>
113    <!-- Derived: Total withdrawals -->
114    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalWithdrawals" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
115        changeable="false" volatile="true" transient="true" derived="true">
116      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
117        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::WITHDRAWAL)->collect(amount)->sum()"/>
118      </eAnnotations>
119    </eStructuralFeatures>
120    <!-- Operation with pre/post conditions -->
121    <eOperations name="withdraw" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean">
122      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
123        <!-- Precondition: Amount must be positive -->
124        <details key="pre" value="amount > 0"/>
125        <!-- Precondition: Must have sufficient funds -->
126        <details key="pre" value="self.balance >= amount"/>
127        <!-- Postcondition: Balance is reduced -->
128        <details key="post" value="self.balance = self.balance@pre - amount"/>
129      </eAnnotations>
130      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
131    </eOperations>
132    <eOperations name="deposit">
133      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
134        <!-- Precondition: Amount must be positive -->
135        <details key="pre" value="amount > 0"/>
136        <!-- Postcondition: Balance is increased -->
137        <details key="post" value="self.balance = self.balance@pre + amount"/>
138      </eAnnotations>
139      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
140    </eOperations>
141  </eClassifiers>
142
143  <!-- TransactionType: Enum for transaction types -->
144  <eClassifiers xsi:type="ecore:EEnum" name="TransactionType">
145    <eLiterals name="DEPOSIT" value="0"/>
146    <eLiterals name="WITHDRAWAL" value="1"/>
147    <eLiterals name="TRANSFER" value="2"/>
148  </eClassifiers>
149
150  <!-- Transaction: Individual transaction record -->
151  <eClassifiers xsi:type="ecore:EClass" name="Transaction">
152    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
153      <details key="constraints" value="positiveAmount validDescription"/>
154    </eAnnotations>
155    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
156      <!-- Invariant: Transaction amount must be positive -->
157      <details key="positiveAmount" value="self.amount > 0"/>
158      <!-- Invariant: Description must not be empty -->
159      <details key="validDescription" value="self.description.size() > 0"/>
160    </eAnnotations>
161    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionId" lowerBound="1"
162        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
163    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionType" lowerBound="1"
164        eType="#//TransactionType"/>
165    <eStructuralFeatures xsi:type="ecore:EAttribute" name="amount" lowerBound="1"
166        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
167    <eStructuralFeatures xsi:type="ecore:EAttribute" name="description" lowerBound="1"
168        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
169    <eStructuralFeatures xsi:type="ecore:EAttribute" name="timestamp" lowerBound="1"
170        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
171    <eStructuralFeatures xsi:type="ecore:EReference" name="account" lowerBound="1" eType="#//Account"
172        eOpposite="#//Account/transactions"/>
173  </eClassifiers>
174</ecore:EPackage>

Step 4

Value constraints validate numeric ranges.

The positiveBalance constraint on accounts and positiveAmount on transactions ensure financial values are never negative.

bank-account.ecore

1<?xml version="1.0" encoding="UTF-8"?>
2<ecore:EPackage xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="Bank" nsURI="http://www.example.org/bank" nsPrefix="bank">
4
5  <!-- OCL Constraints Documentation -->
6  <eAnnotations source="http://www.eclipse.org/emf/2002/GenModel">
7    <details key="documentation" value="Bank Account metamodel demonstrating OCL constraints including invariants, derivation rules, and pre/post conditions."/>
8  </eAnnotations>
9
10  <!-- Bank: Container for customers and accounts -->
11  <eClassifiers xsi:type="ecore:EClass" name="Bank">
12    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
13      <details key="constraints" value="uniqueAccountNumbers uniqueCustomerIds"/>
14    </eAnnotations>
15    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
16      <!-- Invariant: All account numbers must be unique -->
17      <details key="uniqueAccountNumbers" value="self.accounts->isUnique(accountNumber)"/>
18      <!-- Invariant: All customer IDs must be unique -->
19      <details key="uniqueCustomerIds" value="self.customers->isUnique(customerId)"/>
20    </eAnnotations>
21    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
22        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
23    <eStructuralFeatures xsi:type="ecore:EAttribute" name="swiftCode" lowerBound="1"
24        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
25    <eStructuralFeatures xsi:type="ecore:EReference" name="customers" upperBound="-1"
26        eType="#//Customer" containment="true" eOpposite="#//Customer/bank"/>
27    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
28        eType="#//Account" containment="true" eOpposite="#//Account/bank"/>
29  </eClassifiers>
30
31  <!-- Customer: Bank customer with accounts -->
32  <eClassifiers xsi:type="ecore:EClass" name="Customer">
33    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
34      <details key="constraints" value="validEmail adultCustomer"/>
35    </eAnnotations>
36    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
37      <!-- Invariant: Email must contain @ symbol -->
38      <details key="validEmail" value="self.email.indexOf('@') > 0"/>
39      <!-- Invariant: Customer must be at least 18 years old -->
40      <details key="adultCustomer" value="self.age >= 18"/>
41    </eAnnotations>
42    <eStructuralFeatures xsi:type="ecore:EAttribute" name="customerId" lowerBound="1"
43        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
44    <eStructuralFeatures xsi:type="ecore:EAttribute" name="name" lowerBound="1"
45        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
46    <eStructuralFeatures xsi:type="ecore:EAttribute" name="email" lowerBound="1"
47        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
48    <eStructuralFeatures xsi:type="ecore:EAttribute" name="age" lowerBound="1"
49        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"/>
50    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
51        eOpposite="#//Bank/customers"/>
52    <eStructuralFeatures xsi:type="ecore:EReference" name="accounts" upperBound="-1"
53        eType="#//Account" eOpposite="#//Account/owner"/>
54    <!-- Derived: Total balance across all accounts -->
55    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalBalance" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
56        changeable="false" volatile="true" transient="true" derived="true">
57      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
58        <details key="derivation" value="self.accounts->collect(balance)->sum()"/>
59      </eAnnotations>
60    </eStructuralFeatures>
61    <!-- Derived: Number of active accounts -->
62    <eStructuralFeatures xsi:type="ecore:EAttribute" name="activeAccountCount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EInt"
63        changeable="false" volatile="true" transient="true" derived="true">
64      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
65        <details key="derivation" value="self.accounts->select(isActive)->size()"/>
66      </eAnnotations>
67    </eStructuralFeatures>
68  </eClassifiers>
69
70  <!-- AccountType: Enum for account types -->
71  <eClassifiers xsi:type="ecore:EEnum" name="AccountType">
72    <eLiterals name="SAVINGS" value="0"/>
73    <eLiterals name="CURRENT" value="1"/>
74    <eLiterals name="FIXED_DEPOSIT" value="2"/>
75  </eClassifiers>
76
77  <!-- Account: Bank account with balance constraints -->
78  <eClassifiers xsi:type="ecore:EClass" name="Account">
79    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
80      <details key="constraints" value="positiveBalance validAccountNumber sufficientMinimumBalance"/>
81    </eAnnotations>
82    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
83      <!-- Invariant: Balance must not be negative -->
84      <details key="positiveBalance" value="self.balance >= 0"/>
85      <!-- Invariant: Account number must be 10 digits -->
86      <details key="validAccountNumber" value="self.accountNumber.size() = 10"/>
87      <!-- Invariant: Savings accounts must maintain minimum balance -->
88      <details key="sufficientMinimumBalance" value="self.accountType = AccountType::SAVINGS implies self.balance >= self.minimumBalance"/>
89    </eAnnotations>
90    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountNumber" lowerBound="1"
91        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
92    <eStructuralFeatures xsi:type="ecore:EAttribute" name="accountType" lowerBound="1"
93        eType="#//AccountType" defaultValueLiteral="SAVINGS"/>
94    <eStructuralFeatures xsi:type="ecore:EAttribute" name="balance" lowerBound="1"
95        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="0.0"/>
96    <eStructuralFeatures xsi:type="ecore:EAttribute" name="minimumBalance"
97        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble" defaultValueLiteral="100.0"/>
98    <eStructuralFeatures xsi:type="ecore:EAttribute" name="isActive"
99        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean" defaultValueLiteral="true"/>
100    <eStructuralFeatures xsi:type="ecore:EReference" name="bank" eType="#//Bank"
101        eOpposite="#//Bank/accounts"/>
102    <eStructuralFeatures xsi:type="ecore:EReference" name="owner" lowerBound="1" eType="#//Customer"
103        eOpposite="#//Customer/accounts"/>
104    <eStructuralFeatures xsi:type="ecore:EReference" name="transactions" upperBound="-1"
105        eType="#//Transaction" containment="true" eOpposite="#//Transaction/account"/>
106    <!-- Derived: Total deposits -->
107    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalDeposits" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
108        changeable="false" volatile="true" transient="true" derived="true">
109      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
110        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::DEPOSIT)->collect(amount)->sum()"/>
111      </eAnnotations>
112    </eStructuralFeatures>
113    <!-- Derived: Total withdrawals -->
114    <eStructuralFeatures xsi:type="ecore:EAttribute" name="totalWithdrawals" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"
115        changeable="false" volatile="true" transient="true" derived="true">
116      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
117        <details key="derivation" value="self.transactions->select(t | t.transactionType = TransactionType::WITHDRAWAL)->collect(amount)->sum()"/>
118      </eAnnotations>
119    </eStructuralFeatures>
120    <!-- Operation with pre/post conditions -->
121    <eOperations name="withdraw" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean">
122      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
123        <!-- Precondition: Amount must be positive -->
124        <details key="pre" value="amount > 0"/>
125        <!-- Precondition: Must have sufficient funds -->
126        <details key="pre" value="self.balance >= amount"/>
127        <!-- Postcondition: Balance is reduced -->
128        <details key="post" value="self.balance = self.balance@pre - amount"/>
129      </eAnnotations>
130      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
131    </eOperations>
132    <eOperations name="deposit">
133      <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
134        <!-- Precondition: Amount must be positive -->
135        <details key="pre" value="amount > 0"/>
136        <!-- Postcondition: Balance is increased -->
137        <details key="post" value="self.balance = self.balance@pre + amount"/>
138      </eAnnotations>
139      <eParameters name="amount" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
140    </eOperations>
141  </eClassifiers>
142
143  <!-- TransactionType: Enum for transaction types -->
144  <eClassifiers xsi:type="ecore:EEnum" name="TransactionType">
145    <eLiterals name="DEPOSIT" value="0"/>
146    <eLiterals name="WITHDRAWAL" value="1"/>
147    <eLiterals name="TRANSFER" value="2"/>
148  </eClassifiers>
149
150  <!-- Transaction: Individual transaction record -->
151  <eClassifiers xsi:type="ecore:EClass" name="Transaction">
152    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore">
153      <details key="constraints" value="positiveAmount validDescription"/>
154    </eAnnotations>
155    <eAnnotations source="http://www.eclipse.org/emf/2002/Ecore/OCL">
156      <!-- Invariant: Transaction amount must be positive -->
157      <details key="positiveAmount" value="self.amount > 0"/>
158      <!-- Invariant: Description must not be empty -->
159      <details key="validDescription" value="self.description.size() > 0"/>
160    </eAnnotations>
161    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionId" lowerBound="1"
162        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
163    <eStructuralFeatures xsi:type="ecore:EAttribute" name="transactionType" lowerBound="1"
164        eType="#//TransactionType"/>
165    <eStructuralFeatures xsi:type="ecore:EAttribute" name="amount" lowerBound="1"
166        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EDouble"/>
167    <eStructuralFeatures xsi:type="ecore:EAttribute" name="description" lowerBound="1"
168        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
169    <eStructuralFeatures xsi:type="ecore:EAttribute" name="timestamp" lowerBound="1"
170        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
171    <eStructuralFeatures xsi:type="ecore:EReference" name="account" lowerBound="1" eType="#//Account"
172        eOpposite="#//Account/transactions"/>
173  </eClassifiers>
174</ecore:EPackage>

Section 3

Valid Model Instance

A valid model instance satisfies all OCL constraints. Let’s examine a properly structured bank with customers and accounts.

Step 1

Review a valid bank model instance that passes all constraints including unique identifiers, valid emails, adult customers, and proper balances.

valid-instance.xmi

1<?xml version="1.0" encoding="UTF-8"?>
2<xmi:XMI xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI"
3    xmlns:bank="http://www.example.org/bank">
4  <!--
5    Valid Bank Instance
6    This model satisfies all OCL constraints:
7    - Unique account numbers and customer IDs
8    - Valid email addresses (contain @)
9    - Adult customers (age >= 18)
10    - Positive account balances
11    - 10-digit account numbers
12    - Savings accounts maintain minimum balance
13    - Positive transaction amounts
14  -->
15  <bank:Bank name="First National Bank" swiftCode="FNBAUS33">
16    <!-- Customer 1: John Smith, adult with valid email -->
17    <customers customerId="CUST001" name="John Smith" email="john.smith@email.com" age="35">
18      <accounts accountNumber="1234567890" accountType="SAVINGS" balance="5000.00" minimumBalance="100.00" isActive="true">
19        <transactions transactionId="TXN001" transactionType="DEPOSIT" amount="1000.00" description="Initial deposit" timestamp="2025-01-01T10:00:00"/>
20        <transactions transactionId="TXN002" transactionType="DEPOSIT" amount="4000.00" description="Salary credit" timestamp="2025-01-15T09:30:00"/>
21      </accounts>
22    </customers>
23
24    <!-- Customer 2: Jane Doe, adult with valid email -->
25    <customers customerId="CUST002" name="Jane Doe" email="jane.doe@company.org" age="28">
26      <accounts accountNumber="0987654321" accountType="CURRENT" balance="12500.00" minimumBalance="0.00" isActive="true">
27        <transactions transactionId="TXN003" transactionType="DEPOSIT" amount="15000.00" description="Business payment" timestamp="2025-01-02T14:00:00"/>
28        <transactions transactionId="TXN004" transactionType="WITHDRAWAL" amount="2500.00" description="Office supplies" timestamp="2025-01-10T11:45:00"/>
29      </accounts>
30      <accounts accountNumber="1122334455" accountType="FIXED_DEPOSIT" balance="50000.00" minimumBalance="0.00" isActive="true">
31        <transactions transactionId="TXN005" transactionType="DEPOSIT" amount="50000.00" description="Fixed deposit" timestamp="2025-01-05T16:00:00"/>
32      </accounts>
33    </customers>
34
35    <!-- Customer 3: Bob Wilson, exactly 18 (minimum adult age) -->
36    <customers customerId="CUST003" name="Bob Wilson" email="bob.wilson@university.edu" age="18">
37      <accounts accountNumber="5566778899" accountType="SAVINGS" balance="500.00" minimumBalance="100.00" isActive="true">
38        <transactions transactionId="TXN006" transactionType="DEPOSIT" amount="500.00" description="Birthday gift" timestamp="2025-01-03T12:00:00"/>
39      </accounts>
40    </customers>
41  </bank:Bank>
42</xmi:XMI>

Section 4

Invalid Model Instance

Understanding constraint violations helps in designing robust models. Let’s examine a model with intentional violations.

Step 1

Review an invalid bank model instance with intentional violations including duplicate IDs, invalid emails, underage customers, negative balances, and malformed account numbers.

invalid-instance.xmi

1<?xml version="1.0" encoding="UTF-8"?>
2<xmi:XMI xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI"
3    xmlns:bank="http://www.example.org/bank">
4  <!--
5    Invalid Bank Instance - Contains multiple OCL constraint violations:
6
7    1. VIOLATION: Duplicate account numbers (uniqueAccountNumbers)
8       - Account "1234567890" appears twice
9
10    2. VIOLATION: Duplicate customer IDs (uniqueCustomerIds)
11       - Customer ID "CUST001" appears twice
12
13    3. VIOLATION: Invalid email (validEmail)
14       - "invalid-email" does not contain @
15
16    4. VIOLATION: Underage customer (adultCustomer)
17       - Age 16 is less than 18
18
19    5. VIOLATION: Negative balance (positiveBalance)
20       - Balance -500.00 is negative
21
22    6. VIOLATION: Invalid account number length (validAccountNumber)
23       - "12345" is only 5 digits, not 10
24
25    7. VIOLATION: Savings below minimum (sufficientMinimumBalance)
26       - Savings account with balance 50.00 but minimum is 100.00
27
28    8. VIOLATION: Negative transaction amount (positiveAmount)
29       - Amount -100.00 is negative
30
31    9. VIOLATION: Empty description (validDescription)
32       - Empty description string
33  -->
34  <bank:Bank name="Problem Bank" swiftCode="PROBLM33">
35
36    <!-- VIOLATION: Invalid email (no @ symbol) -->
37    <!-- VIOLATION: Underage customer (16 < 18) -->
38    <!-- VIOLATION: Duplicate customer ID "CUST001" -->
39    <customers customerId="CUST001" name="Tommy Young" email="invalid-email" age="16">
40
41      <!-- VIOLATION: Invalid account number (5 digits instead of 10) -->
42      <!-- VIOLATION: Negative balance -->
43      <accounts accountNumber="12345" accountType="CURRENT" balance="-500.00" minimumBalance="0.00" isActive="true">
44
45        <!-- VIOLATION: Negative transaction amount -->
46        <transactions transactionId="TXN001" transactionType="WITHDRAWAL" amount="-100.00" description="Bad withdrawal" timestamp="2025-01-01T10:00:00"/>
47
48        <!-- VIOLATION: Empty description -->
49        <transactions transactionId="TXN002" transactionType="DEPOSIT" amount="50.00" description="" timestamp="2025-01-02T10:00:00"/>
50      </accounts>
51    </customers>
52
53    <!-- VIOLATION: Duplicate customer ID "CUST001" (same as above) -->
54    <customers customerId="CUST001" name="Sarah Connor" email="sarah@future.com" age="30">
55
56      <!-- VIOLATION: Duplicate account number (same as in valid-instance) -->
57      <accounts accountNumber="1234567890" accountType="SAVINGS" balance="1000.00" minimumBalance="100.00" isActive="true">
58        <transactions transactionId="TXN003" transactionType="DEPOSIT" amount="1000.00" description="Valid deposit" timestamp="2025-01-03T10:00:00"/>
59      </accounts>
60
61      <!-- VIOLATION: Savings account below minimum balance -->
62      <!-- Balance 50.00 is less than minimumBalance 100.00 -->
63      <accounts accountNumber="9999888877" accountType="SAVINGS" balance="50.00" minimumBalance="100.00" isActive="true">
64        <transactions transactionId="TXN004" transactionType="DEPOSIT" amount="50.00" description="Small deposit" timestamp="2025-01-04T10:00:00"/>
65      </accounts>
66    </customers>
67  </bank:Bank>
68</xmi:XMI>

Section 5

Running Validation

Use swift-ecore to validate models against their metamodel constraints. The validator reports which constraints are violated and where.

Step 1

Validate the valid instance.

The validator confirms the model satisfies all constraints.

Terminal

1# Validate the valid bank instance against OCL constraints
2swift-ecore validate \
3  --metamodel bank-account.ecore \
4  --model valid-instance.xmi
5
6# Output:
7# Validating model against metamodel constraints...
8#
9# Checking constraint: uniqueAccountNumbers ... PASSED
10# Checking constraint: uniqueCustomerIds ... PASSED
11# Checking constraint: validEmail (Customer: John Smith) ... PASSED
12# Checking constraint: validEmail (Customer: Jane Doe) ... PASSED
13# Checking constraint: validEmail (Customer: Bob Wilson) ... PASSED
14# Checking constraint: adultCustomer (Customer: John Smith, age=35) ... PASSED
15# Checking constraint: adultCustomer (Customer: Jane Doe, age=28) ... PASSED
16# Checking constraint: adultCustomer (Customer: Bob Wilson, age=18) ... PASSED
17# Checking constraint: positiveBalance (all accounts) ... PASSED
18# Checking constraint: validAccountNumber (all accounts) ... PASSED
19# Checking constraint: sufficientMinimumBalance (savings accounts) ... PASSED
20# Checking constraint: positiveAmount (all transactions) ... PASSED
21# Checking constraint: validDescription (all transactions) ... PASSED
22#
23# Validation complete: All 13 constraints satisfied.
24# Model is VALID.

Step 2

Validate the invalid instance.

The validator reports each constraint violation with the affected element and constraint name.

Terminal

1# Validate the invalid bank instance against OCL constraints
2swift-ecore validate \
3  --metamodel bank-account.ecore \
4  --model invalid-instance.xmi
5
6# Output:
7# Validating model against metamodel constraints...
8#
9# Checking constraint: uniqueAccountNumbers ... FAILED
10#   Violation: Duplicate account number '1234567890' found
11#
12# Checking constraint: uniqueCustomerIds ... FAILED
13#   Violation: Duplicate customer ID 'CUST001' found
14#
15# Checking constraint: validEmail (Customer: Tommy Young) ... FAILED
16#   Violation: Email 'invalid-email' does not contain '@'
17#
18# Checking constraint: adultCustomer (Customer: Tommy Young) ... FAILED
19#   Violation: Customer age 16 is less than required minimum 18
20#
21# Checking constraint: positiveBalance (Account: 12345) ... FAILED
22#   Violation: Balance -500.00 is negative
23#
24# Checking constraint: validAccountNumber (Account: 12345) ... FAILED
25#   Violation: Account number '12345' has 5 digits, expected 10
26#
27# Checking constraint: sufficientMinimumBalance (Account: 9999888877) ... FAILED
28#   Violation: Savings balance 50.00 is below minimum 100.00
29#
30# Checking constraint: positiveAmount (Transaction: TXN001) ... FAILED
31#   Violation: Transaction amount -100.00 is negative
32#
33# Checking constraint: validDescription (Transaction: TXN002) ... FAILED
34#   Violation: Transaction description is empty
35#
36# Validation complete: 9 constraint violations found.
37# Model is INVALID.

Check Your Understanding

Question 1 of 3

What does the OCL expression accounts->isUnique(a | a.accountNumber) check?

That all account numbers are different from each other

The isUnique operation verifies that the expression evaluates to a distinct value for each element in the collection.

That at least one account has a unique number

That would be exists. The isUnique operation checks ALL elements have distinct values.

That account numbers are formatted correctly

Format validation would use string operations like size(). This checks uniqueness.

Question 2 of 3

How would you express “all customers must have positive account balances”?

customers->exists(c | c.accounts->forAll(a | a.balance > 0))

This only requires ONE customer to have all positive balances. We need ALL customers.

customers->forAll(c | c.accounts->forAll(a | a.balance > 0))

This requires that for ALL customers, ALL their accounts have positive balances.

customers.accounts->select(a | a.balance > 0)->notEmpty()

This only checks if there’s at least one positive balance, not that all are positive.

Question 3 of 3

When is a constraint considered satisfied?

When its OCL expression evaluates to true

OCL constraints are boolean expressions. A constraint is satisfied when it evaluates to true for the model.

When no exception is thrown during evaluation

Even if evaluation succeeds, the constraint fails if the result is false.

When the model can be serialised to XMI

XMI serialisation doesn’t validate OCL constraints. Explicit validation is required.

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