On 03/04/15 03:47, Qihong Lin wrote:
Hello Andy,
It's submitted in time.
Good.
Ying - what is the next process step?
I saw your notes, thanks. Here're some further
questions.
1) API of QueryExecution
Does the API look like:
- Iterator<Quad> QueryExecution.execConstrucQuads()
- Dataset QueryExecution.execConstructDataset()
Both. (One builds on the other anyway.)
It should mirror how execConstruct/execConstructTriples are done unless
there is a very good reason not to.
2) master.jj
How does master.jj generate arq.jj? What tool? You mentioned "is
processed with cpp". What's cpp?
cpp is the C preprocessor (yes!!) It rewrites one text file to another
text file. ARQ does not cpp macros, it is just using defined symbols
ARQ and SPARQL_11 to put in different blocks of text.
It's also why there are no comments in arq.jj. cpp removes them and
blank lines (the alternative is lots of blank lines - it's yuk).
The script to drive it is jena-arq/Grammar/grammar (it's a bash script -
I don't know how well it runs on MS Windows - it used to using cygwin).
The script directs the output to the right place in the java source code.
If you have trouble running it, edit arq.jj then run javacc.
The SyntaxARQ parts that are not SPARQL 1.1, are in sections
#ifdef ARQ
....
#endif
3) query string sytax
I went through TriG syntax.
- For our query string, can it construct a Dataset with multiple
graphs, or just one default/named graph?
Multiple.
A dataset is one default and zero or more named graphs.
CONSTRUCT
{ GRAPH :g1 { ?s ?p ?o }
GRAPH :g2 { ?s ?p ?o }
GRAPH ?g { ?s ?p ?o }
} ...
only in real use the patterns will be bigger.
- Shall we consider using variables for named graphs? I mean "?g", not ":g":
CONSTRUCT {
# Named graph
GRAPH ?g { ?s :p ?o }
} WHERE
Yes.
Class Template can be made to work purely on quads. Where it current
uses BasicPattern (which is triples), use QuadPattern.
That will work for non-extended SPARQL 1.1 as well because "CONSTRUCT {
no use of GRAPH }" will give a quad pattern of all quads for the default
graph. There is a magic constant for "this quad is for the default
graph" - see class Quad.
So you don't need tow different sets of machinary - update Template to
handle quads and the syntactic restrictions of SPARQL_11 will stop it
getting named graph in CONSTRUCT.
execConstruct/execConstructTriples then work on the default graph of a
dataset.
You may find it helpful to look at the TriG parser output. That parser
is not Javacc (it's much faster). It's informing but you will need to
write the javacc for this project.
regards,
Qihong
Andy
