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Re: DASL Spec

From: Eliot Christian <echristi@usgs.gov>
Date: Sun, 07 Nov 1999 06:14:19 -0500
Message-Id: <4.2.0.58.19991107055734.009e9f00@opsmail.er.usgs.gov>
To: www-webdav-dasl@w3.org
I am involved in the W3C XML Query work, which has a specific 
requirement to coordinate with the IETF DASL work. The XML 
Query work needs to address protocol issues up front and also 
needs to document some Use Cases to help focus the work.
  
I offer for consideration the following Use Case as a way 
to introduce some of the protocol considerations of an 
application using XML Query. I would very much like to know 
if you think this makes sense from the DASL perspective, 
and especially any specific suggestions to improve it ;-)

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XML Query Use Case: Referral Search

In this case, the user of XML Query begins with a text 
search at a referral service, using just one English word. 
This results in a number of candidate collections, each one 
titled and ranked by score. The user selects a collection 
and gets a more precise search facility that is particular 
to the selected collection. The user constructs a Boolean 
XML Query and then receives a set of document scores and 
titles which satisfy the query. 

A narrative of the interactions involved in this case is 
provided below, numbered as steps alternating between client 
and server. (Specific syntax and storage mechanisms are not 
meant to be implied by this narrative.)

(1) Client - The user designates that query processing is 
to be performed by a particular service (e.g. host:port) 
and a particular collection of XML documents (e.g., named 
structure in a file system). The client offers a facility 
to construct an XML Query consisting of words in English. 
The client sends the user's query to the designated service.

(2) Server - The designated service processes the query 
against the designated collection of XML documents, applying 
criteria appropriate for a full-text search. The service 
causes delivery to the client of XML representing a named 
"result set" pointing to XML documents within the collection 
that satisfy the query. Each member of the result set has a 
structure composed of a score for the set member, a name for 
the set member, and a handle for retrieving the set member 
(e.g., URL). 

(3) Client - The client presents to the user the result set 
XML document delivered from the query processing in step 2. 
When the user selects a particular member of the result set, 
the client causes delivery to the original service of a 
second XML Query. In this second query, the query is to be 
processed against the result set constructed in step 2, and 
the querying is to select the specific set member based on 
the retrieval handle supplied.

(4) Server - The service retrieves the XML document 
designated by the set member retrieval handle and causes 
delivery of the XML document to the requesting client. 
This XML document itself describes another collection of XML 
documents available on a service elsewhere. Its structure 
includes a service title, a pointer to the schema for the 
collection, and a handle for accessing the collection 
(e.g., a URL including the service host:port and named 
structure in a file system).

(5) Client - The client presents to the user the retrieved 
XML document delivered from the process in step 4. When the 
user selects the handle for accessing the described 
collection, the client retrieves the collection schema from 
the network and presents to the user a facility to construct 
an XML Query. This facility now includes search constraints 
based on the schema, not only full-text but title, 
originator, subject, date, and place. The user constructs 
a Boolean search and this XML Query is delivered to the 
referred service and collection.

(6) Server - The designated service processes the query 
constructed in step 5 against the designated collection of 
XML documents, applying the Boolean search criteria using 
the structure in the XML schema. The service causes delivery 
to the client of an XML document pointing to a number of XML 
documents that satisfy the query.

--------------------------------------------------------- 


Eliot Christian, US Geological Survey, 802 National Center, Reston VA 20192
echristi@usgs.gov  Office 703-648-7245  FAX 703-648-7112  Home 703-476-6134
Received on Sunday, 7 November 1999 07:13:45 GMT

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