Reuse using Abstract Rules

Roger Costello

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Motivation for Abstract Rules

• Suppose you have some assertions that are used by several rules.
• Rather than repeating those assertions in each rule, it would be beneficial to place them into an "abstract rule" where they can be reused.
• A rule reuses the assertions by extending the abstract rule.
• Thus, abstract rules provide a mechanism for reusing assertions.

How to Create an Abstract Rule

• Omit the context attribute
• Add an attribute "abstract" with a value "true"
• Identify the rule using an "id" attribute
• This document shows a series of daily activities. For each activity we would like to check that the activity finished *after* starting.

Example Abstract Rule

1. <sch:rule abstract="true" id="start-finish">
2. <sch:assert test="finish > start">
3. You must finish after you start
4. </sch:assert>
5. </sch:rule>

How to use an Abstract Rule

• Create a rule; set the context attribute.
• Within the rule nest an <extends> element, with a rule attribute whose value is the identifier of an abstract rule.

Example of using an Abstract Rule

1. <sch:rule context="eat-breakfast">
2. <sch:extends rule="start-finish" />
3. </sch:rule>

• View the entire collection of rules: Daily-Activities.sch

Reuse Plus Extends

• In the previous example each rule just used the assertions in the abstract rule.
• However, a rule can reuse the assertions in the abstract rule and add additional assertions, e.g.

1. <sch:rule context="eat-breakfast">
2. <sch:extends rule="start-finish" />
3. <sch:assert test="finish < start+15">
4. Breakfast must not exceed 15 minutes
5. </sch:assert>
6. </sch:rule>