Subject: DASL - who wants to use it? (requirements spec?)

From: Alan Kent <[email-masked]>
Date: Fri, 7 Dec 2001 19:25:23 +1100

I remember the recent question about DASL (was it this list?).
I was wondering if part of the problem with DASL is the question
of whether it addresses a need, or addresses it appropriately.

We have a text searching engine that can do lots of funky searches
etc. on the content of resources using fields (lets say dublin
core elements). But this would be quite a different thing to
querying on WebDAV properties.

Hence I was interested to understand better the goal of DASL.
Is it to be able to query WebDAV properities (and nothing else).
Or was it intended to be broader and cover the harder problem
of querying content as well?

Just curious to understand the intended scope better before
I jump in. I found a reference to a dasl requirements document
(I have not looked it up yet). But is it still valid? I ask
only because if its been a while and if no one has implemented
it, is it because they have been busy, or because DASL has
missed the mark in some way?

Alan

ps: I noticed that DASL seems to allow other queries to be
plugged in. While this is good, for the above I am not after
an answer like "you can do anything you like". I am more
interested in "what do people like/want?"

pps: I also noticed that the "basic" query langauge looked
rather long when you got down to it - orderby, contains, like,
three value logic... Convienient if you have an SQL engine around
I guess.

---

From: "Lisa Dusseault" <[email-masked]>
Date: Mon, 17 Dec 2001 10:37:33 -0800

Not sure if anybody ever answered your basic question about whether DASL
addresses content querying.  It does.

Here is the query fragment that would search the body of a document:
<D:where>
  <D:contains>Peter Forsberg</D:contains>
</D:where>

This is similar to the property queries, but it does not name a property,
therefore it's the content that must be searched for the string.

Note that it's possible to do exact string matching ("Peter Forsberg") and
string-by-string matching ("Peter" and "Forsberg", not necessarily
together).  Section 5.13.1 of DASL shows both examples.

Lisa

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Alan Kent
> Sent: Friday, December 07, 2001 12:25 AM
> To: WebDAV
> Subject: DASL - who wants to use it? (requirements spec?)
>
>

---

From: "Julian Reschke" <[email-masked]>
Date: Mon, 17 Dec 2001 20:22:02 +0100

> [mailto:[email-masked]]On Behalf Of Lisa Dusseault
> Sent: Monday, December 17, 2001 7:38 PM
> To: Alan Kent; WebDAV
> Subject: RE: DASL - who wants to use it? (requirements spec?)
>
>

Lisa,

which version are you referring to? According to [1],

- "contains" is an optional operator (so cou can't rely on it being
supported)
- the method of matching is only loosely defined; in particular you can't
rely on it doing "exact" matching.

[1] <http://www.webdav.org/dasl/protocol/draft-dasl-protocol-00.html>

---

From: "Lisa Dusseault" <[email-masked]>
Date: Mon, 17 Dec 2001 16:28:59 -0800

> - "contains" is an optional operator (so cou can't rely on it being
true

> rely on it doing "exact" matching.

true.

> [1] <http://www.webdav.org/dasl/protocol/draft-dasl-protocol-00.html>

I was looking at the same draft.  But I think Alan wanted to know if DASL
addressed body content searching at all, which it does.  If the server
supports it, the client can use it (as usual).

lisa

---

From: Alan Kent <[email-masked]>
Date: Tue, 18 Dec 2001 16:53:21 +1100

> supports it, the client can use it (as usual).

This may be a bit of a can of worms, but is there any interest in using
the structure of content in queries? For example, being able to query
on the content's "Title" or "Author". I am thinking of Dublin Core
metadata sort of approach - not XPath or XML Query since the content
can be anything (PDF, GIF, etc). Allowing something like Dublin Core
would allow a level of structure to be imposed.

If this was considered useful, would the better approach be to define
additional live properites that were automatically extracted from the
content (hence its really just querying on properties after all, not
content itself), or to allow querying on properties or content.
I guess I am sort of asking should <allprops> return the Dublin Core
like elements too? (It could be expensive to compute).

I do a fair bit of work with a search and retrieval protocol, Z39.50.
It is based on the Dublin Core idea of separating your access points
for searching from the physical representation of the data. It allows
querying on "Title" as an abstract concept, without requiring that
it be possible to return a "Title" out from the data. It takes a
different view on query capabilities too - it says you have terms
that can have constraints applied. Specifying a property name to
search within is a constraint. Specifying > (greater than) is a 
constraint. It does not use 3 value logic. It more says 'return
all records that contain some data that match the condition'.
WebDAV might not have the same problem of repeating values as
properites have only one value.

Personally I would like to search on parts of the content using
Dublin Core (or other) metadata standards. Should I do this using
WebDAV properties bound to parts of the content of the resource?
Any other ideas?

Thanks
Alan

ps: I am not likely to do this any time soon. Just thinking about
the future.