Before you start
This tutorial shows how to use the Autonomic Computing Expression Language (ACEL), an XML-based expression language, to create an expression, parse it, prepare input for it, and evaluate it. ACEL was originally developed as a part of the Autonomic Computing Policy Language to describe conditions when a policy should be applied to a managed system. To learn more about how policies can be used to manage an IT system, download IBM® Policy Management for Autonomic Computing (PMAC) from alphaWorks. (See Resources for more information.) However, ACEL is applicable in many other contexts such as specifying service level agreements, pricing, scheduling, and provisioning of services. In general, ACEL can be used to specify various types of expressions (numeric expression, Boolean expression, string expression, and so on) in XML documents.
The distinguishing features of ACEL are:
- ACEL provides a rich set of datatypes and functions, allowing a simple representation of most expressions required for system management.
- ACEL is a strongly typed language, and its XML schema enforces most of the type constraints. As a result, ACEL expressions can be validated in plain XML editors to allow easy authoring of ACEL expressions.
- ACEL can be extended by a deployer such that it retains its typed property. Therefore, even the extended ACEL expressions can be validated in a plain XML editor.
- ACEL includes a comprehensive time zone specification, with date and time values allowing unambiguous treatment of time instances even in the presence of daylight saving time.
This tutorial is for an intermediate-level software developer who wants to acquire knowledge of how to embed ACEL expressions in XML files and use them for various applications such as business rules and policy management. The prerequisites for taking the tutorial are a basic knowledge of Java programming and a general understanding of XML schema and processing. You can download the examples in this tutorial, the ACEL JAR file, and the companion document ACEL User's Guide , which presents the complete syntax and semantics of the ACEL expressions with examples. See Resources for more information.
To run the examples in this tutorial, you must install the Java Runtime Environment (JRE) Version 1.4.x. See Resources for links to appropriate run-time environments.
The specific examples in the tutorial are written for IBM WebSphere® Studio Application Developer (Application Developer). You can download a trial version of IBM WebSphere Studio Application Developer. Other Java programming environments can be used, but the required steps might be different than those shown in the tutorial.