How many types of declarative rules are there in Pega?

 Declarative rules in Pega

In Pega, four main types of declarative rules in pega automate and manage business logic without requiring procedural code.These rules help to ensure consistency and accuracy in the application.

  • When using a declarative rule, we don’t need to call and execute it automatically.
  • You can create these rules under the Decision Category.

Declarative Processing:  Declarative rules process automatically without requiring explicit calls, managed by the process commander.

  • When we create a declarative rule and leave it without referring to any other rule,.
  • When we create a declarative rule, we will include properties in the definition.
  • Declarative rules execute immediately upon using properties or updating values.
  • These rules automatically execute when using the properties involved in declarative rules.

Types of Declarative Rules in Pega:

  1. Declaration Expression
  2. Constraints/Declare Constraints
  3. Declare On Change
  4. Declare Trigger: This auto-executes when a DB table action is performed.
  5. Declare Index: This auto-executes when a DB table action is performed.
  6. Data Pages (Declare Pages).

Working with Declare Constraint: Creating “Declare Constraint” for age validation based on gender

Additionally, you can create constraint rules under the Decision Rule category. (Create->Decision->Constraints).

 Declarative rules in Pega
Declarative rules in Pega

1. Declare expressions

  • Purpose: Automatically compute the value of a property based on expressions involving other properties.
  • Usage: Commonly used to derive values, perform calculations, or set default values dynamically.
  • Example: If you have a property with a total cost, it can be set to the sum of the base cost and tax amount using a declare expression.  When the base cost or tax amount changes, the system automatically recalculates the total cost.

Advanced Features:

  • Scope: You can specify whether an expression applies globally or only within a certain context.
  • Backward Chaining: In some cases, Pega uses backward chaining, where the value is calculated only when it is needed (on demand).

2. Declare Constraints

  • Purpose: Enforce business rules by validating the values of properties.
  • Usage: Used to ensure data integrity and adherence to business policies by restricting the values that properties can take.
  • Example: You might have a constraint that a property age must be greater than 18. If a user tries to set age to a value less than 18, the system will generate an error message and prevent the change.

Advanced Features:

  • Message Severity: Constraints can specify different levels of severity for validation messages, such as warnings or errors.
  • Preconditions: Constraints include conditions to control when to apply the validation.

3. Declare an OnChange

  • Purpose: Execute specific actions when the value of a property changes.
  • Usage: Useful for triggering updates or validations in response to property changes without needing explicit procedural code.
  • Example: If a property status changes to “Approved,”  you might trigger an activity that sends an approval email or logs an entry in an audit trail.

Advanced Features:

  • Conditionally Triggered Actions: Actions can be triggered based on specific conditions being met.
  • Multiple Actions: You can configure multiple actions to execute in sequence when a property changes.

4. Declare a trigger

  • Purpose: Automatically execute activities when specific events occur in the database, such as record creation, updates, or deletions.
  • Usage: Used to maintain data consistency, perform background processing, or synchronize data across systems.
  • Example: When creating a new customer record, a declare trigger can automatically assign a customer ID, send a welcome email, and update a marketing database.

Advanced Features:

  • Event Types: Triggers can be set to fire on different types of database events, such as insert, update, or delete.
  • Execution Order: You can control the order in which multiple triggers execute.

Benefits of Declarative Rules in Pega

 Declarative rules in Pega
Declarative rules in Pega
  • Simplicity: Declarative rules reduce the need for manual coding, making the application easier to develop and maintain.
  • Consistency: Ensures consistent application of business rules and calculations across the application.
  • Reactivity: Declarative rules respond automatically to changes in the application, providing real-time updates and validations.
Best Practices for Using Declarative Rules
  1. Use Declarative Rules Judiciously: While declarative rules offer powerful automation, overuse can lead to complex and hard-to-trace dependencies. Use them where they provide clear benefits.
  2. Document Rules Clearly: Ensure that the purpose and logic of each declarative rule are well-documented to aid future maintenance.
  3. Monitor Performance: Declarative rules can have performance implications, especially in large or complex applications. Regularly monitor.
  4. Testing and Validation: Thoroughly test declarative rules in various scenarios to ensure they work as expected and do not introduce unintended side effects.
Case Studies and Examples
  Financial Calculations
  • Scenario: A financial application needs to automatically calculate loan interest based on changes to the principal amount and interest rate.
  • Solution: Use Declare Expressions to calculate the interest whenever the principal or interest rate changes, ensuring real-time accuracy.
 Data Integrity in HR Systems
  • Scenario: An HR application needs to validate employee data, such as ensuring that the age is above 18 and the email address is in a valid format.
  • Solution:  Implement declared constraints to automatically enforce these validations whenever employee data is entered or modified.
 Automated Notifications
  • Scenario: A customer service application needs to send notifications when the status of a service request changes.
  • Solution: Use Declare OnChange rules to trigger email notifications whenever the status property changes, ensuring timely communication with customers.


In conclusion, Declarative rules in Pega streamline the process of managing business logic by automating calculations, validations, and triggers.

By leveraging these rules, developers can create more efficient, consistent, and maintainable applications.

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