Mike Beckerle created DAFFODIL-2620:
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Summary: Redesign runtime 1's nextElementErd()
Key: DAFFODIL-2620
URL: https://issues.apache.org/jira/browse/DAFFODIL-2620
Project: Daffodil
Issue Type: Improvement
Components: Back End, Middle "End"
Affects Versions: 3.2.1
Reporter: Mike Beckerle
The conversion of textual representations of Infosets (such as XML or JSON)
requires converting local name+namespace into an ERD.
This currently depends on a data structure called the 'TRD Stack' which must be
carefully maintained by the runtime. Each term on the TRD stack has a
PartialElementResolver and the first such on the TRD stack which resolves the
element "wins" and provides the ERD.
This algorithm enables shared group definitions, and shared complex type
definitions (which implicitly contain shared group definitions), to have
different resolution of elements based on the specific context where they are
used.
For example, suppose a shared sequence group contains an optional element child
named C. Suppose it is used in two different places, one where the shared
sequence is followed by a required element named A, the other a required
element named B.
Then at runtime, in one context, the nextElementErd() will consider the
possibility of either C or A, the other context the nextElementErd() will
consider the possibility of C or B. C will be the term on top of the TRD stack,
and in the first context, the next thing on the TRD stack will be the term
containing A. In the other context the next thing on the TRD stack will be the
term containing B. By chaining down the stack calling each
PartialElementResolver, we're able to have a compiled data structure for our
shared sequence group which is context independent, and so can in fact be
shared.
However, there is much complexity here.
Each point-of-use of a shared component contains two aspects. The shared
aspect, and the specific-to-that-point-of-use aspect. By associating the
nextElementErd() data structures not with the shared aspect, but with the
specific aspect, the need for the TRD stack can be eliminated, replaced by a
static data structure.
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