Retrieving Compound Elements


Issue raised by: Simon Marshall; [email protected]; Tue, 10 Dec 1996 11:04:57 GMT


Synopsis:
What is implied when an element spec in a Present requests a non-leaf (i.e. structured) element. For example, suppose an Abstract Record Structure defines:
(4,1): Fubar
(4,1)/(4,2): Foo
(4,1)/(4,3): Bar
Is the simpleElement comprising a specificTag of (4,1) equivalent to a, say, sequence of simpleElement comprising (4,1)/(4,2) and (4,1)/(4,3)? Or, to retrieve the two elements Foo and Bar, should (4,1)/wildPath be used?

Response:
A request for (4,1) is equivalent to requesting the two subelements individually. See RET.3.1.1 second paragraph, last sentence.

wildPath won't work. It is explicitly precluded from occuring at the end of a path (see last sentence of comment on wildPath in ASN.1 for eSpec-1). WildPath matches the end of a path. It could be used, for example, to retrieve all (and only) captions, where the tag for captions is known, and where captions are spread throughout a document at various levels of its hierarchy.

wildThing, on the other hand, would work for the specific case cited, using an occurrence value of 'all'. However, this is not what wildThing was intended for, and using (4/1) is sufficient and simpler than (4,1)/wildThing[all].


Status: Approved (4/97)
Library of Congress
Library of Congress Help Desk (05/01/97)