One of the most common points of confusion I hear about in the S1000D industry is concerning what the BREX data module does and how S1000D business rules are used to generate a BREX data module. It is believed by some that a BREX DM contains all of the business rules for a program, and by handing a BREX to a partner company, you can effectively instruct them on how to develop S1000D to conform to your business rules.
This is not completely accurate. A BREX document is really only capable of storing rules that are enforceable on the actual S1000D XML content. This is due to the fact that a BREX rule must be enforced via an XPath statement. Decisions pertaining to the use of optional elements are perfect examples of S1000D business rules that exist in, and are enforced by, the BREX.
Rules governing the overall usage of S1000D cannot be enforced or expressed in the BREX data module. Examples of such rules include:
- the decision to use process data modules instead of the fault isolation data module, or
- to use an Arial font instead of Times for chapter titles.
Although these are important rules, they cannot be expressed using an XPath statement and, thus, are not included in the BREX document.
When conducting training classes or when explaining S1000D constructs to our customers, we have found it useful to think of S1000D business rules as consisting of two distinct categories:
- Program Rules
- Authoring Rules
A program rule is an S1000D business rule that dictates specific usages of the standard that does not specifically address XML content. Program rules include rules such as graphic formats, CSDB configuration, type of data modules to be used, etc. As program rules are meant solely for human use, these are generally provided as documentation (a Word file, HTML, etc).
Authoring rules are data oriented and can be expressed as an XPath statement and, as such, can be enforced by a program or software application. The decision to disallow an optional element can be enforced via an XPath statement, and thus should be included in your BREX document. It is then the duty of a BREX-aware processor to read the BREX document and enforce these authoring rules.
So, when exchanging business rules, it is important to not only exchange your BREX data module, but supporting documentation containing program rules as well.
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