Defining extensible expression behavior in a rules system

• US 20080059269A1
• Filed: 08/30/2006
• Published: 03/06/2008
• Est. Priority Date: 08/30/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Willis, Jurgen A., McCrady, Donald J., Rummell, John A.
• Granted Patent: US 7,970,723 B2
• Time in Patent Office: Days
• US Class Current: 705/8
• CPC Class Codes: G06Q 10/06316 Sequencing of tasks or work
• CPC Class Codes: G06Q 10/10 Office automation; Time management

Abstract

Described herein is technology for, among other things, enabling use of custom expressions in a rules engine. The rules engine may be used in conjunction with a workflow. The technology involves providing a custom expression with access to validation context and execution context of the workflow. The custom expression can then participate in rules engine validation and execution. Furthermore, the technology allows for variables of the custom expression to be analyzed so that the rules engine can discover the variable dependencies of the custom expression and any side effects that drive forward chaining.

Claims

1. A method for enabling use of a custom expression in a rules engine, the method comprising:

providing the custom expression with access to validation context;

validating the custom expression using the validation context; and

if the custom expression passes validation;

determining which variables the custom expression reads from or writes to;

providing the custom expression with access to execution context; and

evaluating the custom expression.

2. The method as recited in claim 1 wherein the custom expression is defined by an expression tree and the method further comprises:

decompiling the expression tree into a string representation of the custom expression.

3. The method as recited in claim 1 further comprising:

comparing the custom expression with a second expression to determine if a portion of the custom expression and the second expression are the same.

4. The method as recited in claim 1 further comprising:

creating a clone of the custom expression.

5. The method as recited in claim 4 further comprising:

providing a user interface for editing the clone.

6. The method as recited in claim 1 further comprising:

receiving a string representation of the custom expression; and

parsing the string representation into a form understood by the rules engine.

7. The method as recited in claim 6 wherein the string representation comprises an expression type, wherein further the expression type comprises a public constructor that takes a parameter that is understood by the rules engine.

8. The method as recited in claim 1 wherein the validation context comprises access to:

type information and expression information that have been discovered through previous validation processes;

a target type that the custom expression is going to be executed against; and

errors that have occurred in previous validation processes.

9. The method as recited in claim 1 wherein the execution context comprises access to:

variable dependency information describing variable dependencies between the custom expression and a second expression;

an instance of the object that is being evaluated;

runtime services of the instance;

type information and expression information that have been discovered through previous validation processes;

a target type that the custom expression is-going to be executed against; and

errors that have occurred in previous validation processes.

10. The method as recited in claim 1 wherein said determining generates usage information and the method further comprises:

discovering variable dependencies between the custom expression and a second expression using the usage information;

re-evaluating the custom expression if the second expression changes a variable that the custom expression reads from; and

re-evaluating the second expression if the custom expression changes a variable that the second expression reads from.

11. The method as recited in claim 1 further comprising:

validating a sub-expression of the custom expression;

determining which variables the sub-expression reads from or writes to; and

evaluating the sub-expression.

12. A system comprising:

a rules engine for managing rules;

a custom expression;

a validation interface for interfacing between the custom expression and the rules engine, wherein the validation interface is configurable to access validation context provided by the rules engine, wherein further the validation interface is configurable to validate the custom expression using the validation context;

an evaluation interface for interfacing between the custom expression and the rules engine, wherein the validation interface is configurable to access execution context provided by the rules engine, wherein further the evaluation interface is configurable to evaluate the custom expression; and

a usage analysis interface for interfacing between the custom expression and the rules engine, wherein the usage analysis interface is configurable to analyze the usage of variables by the custom expression and provide usage information to the rules engine.

13. The system as recited in claim 12 wherein the custom expression is defined by an expression tree and the system further comprises:

a decompile interface for interfacing between the custom expression and the rules engine, wherein the decompile interface is configurable to decompile the expression tree into a string representation of the custom expression.

14. The system as recited in claim 12 further comprising:

a comparison interface for interfacing between the custom expression and the rules engine, wherein the comparison interface is configurable to compare the custom expression with a second expression to determine if a portion of the custom expression in the second expression are the same.

15. The system as recited in claim 12 further comprising:

a replication interface for interfacing between the custom expression and the rules engine, wherein the replication interface is configurable to create a clone of the custom expression; and

a user interface for editing the clone.

16. The system as recited in claim 12 further comprising:

a parser for parsing a string representation of the custom expression into a form understood by the rules engine.

17. The system as recited in claim 12 wherein the rules engine is configurable to discover variable dependencies between the custom expression and a second expression using usage information obtained from the usage analysis interface, wherein further the rules engine is configurable to re-evaluate the custom expression if the second expression changes a variable that the custom expression reads from, and wherein further the rules engine is configurable to re-evaluate the second expression if the custom expression changes a variable that the second expression reads from.

18. A computer-usable medium having computer-readable program code stored thereon for causing a computer system to execute a method for enabling use of a custom expression in a rules engine, comprising the steps of:

(a) receiving a call associated with a particular expression;

(b) determining whether the expression is custom;

(c) if the expression is custom;

(i) validating the expression;

(ii) analyzing the usage of variables by the custom expression; and

(iii) evaluating the expression.

19. The computer-usable medium as recited in claim 18 wherein the custom expression is defined by an expression tree and the method further comprises the steps of:

(d) decompiling the expression tree into a string representation of the custom expression;

(e) creating a clone of the custom expression;

(f) providing a user interface for editing the clone;

(g) receiving a string representation of the custom expression;

(h) parsing the string representation into a form understood by the rules engine; and

(i) comparing the custom expression with a second expression to determine if a portion of the custom expression and the second expression are the same.

20. The computer-usable medium as recited in claim 19 further comprising the steps of:

(j) evaluating the portion for one of the custom expression and the second expression; and

(k) replicating the result of the evaluation of the portion for the other of the custom expression and the second expression.