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Tag Inheritance Chains

As previously touched upon, the declarations in GPD's may be linked together so that one GPD reuses some portion of another GPD. This is accomplished by a kind of inheritance policy, whereby a tag may be resolved by following a link rather than examining an attribute value. The tag value is then looked up in the GPD linked to. The declarations to carry this out are in the `indirect references' section of each section of the GPD. Each declaration consists of the name of the tag to inherit and a link to the GPD from which the tag is being inherited. Note that this MUST be a link, not simply the name of the GPD.

If the STRUCTURE declaration is indirect in this way, then the subsequent definitions relating to the indirect tag are completely resolved using the indirection. That is, if the inheritance is in the STRUCTURE section, then all other sections (ACCESS, EXPAND, FORMAT, AUTOLINKS) are also inherited. However, if the inheritance is in the ACCESS, FORMAT, AUTOLINKS, or EXPAND declarations, the inheritance is valid only for that section.

As an example, compare the `document overview' GPD declarations of paragraph and title in figure 7.32.

 


:  The `document overview' GPD

As you see, the `paragraph' concept inherits its STRUCTURE from the text GPD, and therefore it has the same `behaviour' whether in the `document overview' or `text' view. The `title' concept inherits only the ACCESS declaration from the `text' GPD, and therefore its STRUCTURE, FORMAT, and EXPAND declarations are taken from the `document overview' GPD rather than the `text' GPD. One result of this is that in the `document overview' view expanding on the title will expand the corresponding section, because the EXPAND declaration for `title' states that a `title' should be expanded as `text'. On the other hand, if `title' inheritance were done in the STRUCTURE section, the EXPAND section would be taken from the `text' GPD, which states that a `title' should be expanded in `document contents' view. Note that if you wish to see what is being inherited, you can expand on the name of the GPD in the `indirect references' section after the name of the concept being inherited.



next up previous contents index
Next: System Defined GPD's Up: NOTES on Generic Previous: GPD Maps



Martin Sjolin
Mon May 29 19:53:45 MET DST 1995