- From: Julian Reschke <julian.reschke@gmx.de>
- Date: Wed, 13 Jun 2001 12:24:24 +0200
- To: "Babich, Alan" <ABabich@filenet.com>, <w3c-dist-auth@w3.org>
Alan, first of all: thanks for the feedback. > From: w3c-dist-auth-request@w3.org > [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Babich, Alan > Sent: Tuesday, June 12, 2001 10:14 PM > To: 'Julian Reschke'; w3c-dist-auth@w3.org > Subject: RE: Moving DASL to Experimental > > > (1) DASL is NOT completely silent about how the grammar engine is > supposed to know about data types. > (2) DASL deliberately punted on querying hierarchical data types, i.e., > so called "structured" data types, so that we could get the first > draft out > in a timely manner. The plan was to address the structured properties > on the next draft. If you think about it, that might still be the best > approach. > > Re point (1): By DBMS standards, WebDAV has an inadequate > property model. You can not even say that a property has a > given data type. In the WebDAV proposal, examples are given wherein Agreed. Some do, some don't. A property "x" may have different types for different resources. And so on... > a property changes data type (for example, if the name of > the property leads you to believe it is a certain data type, say, > integer, and a collection doesn't implement it, the collection can > return a string that says "not implemented"). WebDAV got away without Are you referring to some live property? I don't think this is the case for any property defined in RFC2518. > a rigorous property model until it came time to query, i.e., DASL. At that > point > one can no longer duck the issue. (For example, even users that are > computer illiterate know that "2" comes after "10" if both are > strings, but > before if both are integers.) Another problem was that at the > time DASL was > developed, XML lacked the notion of data types, but there was an XML > effort underway to introduce data types. So, everyone wanted the > XML effort > to be the way of introducing data types, rather than getting them > in through > the back door via DASL, probably in a way that didn't quite track > the XML effort due to lack of resources and time. What you're saying is that there were good reasons for the spec to be silent about these issues. I don't argue with the approach, I just state that it's a problem if you actually want to implement DASL. > What DASL said about data types is the following. First, you can > have a query schema that describes the properties, including their Query schemas were taken out of the spec, right? AFAIK, the "current" one is at <http://www.webdav.org/dasl/protocol/draft-davis-dasl-protocol-00.html>, and Query Schemas were taken out because they seemed to be too complex at this point of time. > data types. The data types included Boolean, string, int, float, and > dateTime. Second, if you don't have a query schema, or if the > data type of a property is not given, the property defaults to > type string. > A literal compared to a property in a query must be coercible to the type > of the property. Third, people believed that in 90+% of the applications, > knowledge of the properties would be hard wired into the application. > Certainly, that would be true for properties defined by DAV, e.g., > getcontentlength. That is why the query schema was made optional. (actually it was removed, and I wasn't really aware anymore of Query Schema when I wrote that mail). So some more points (in random order): - with QS being removed, I think it would be good if the spec for DAV:basicsearch would actually define how comparisons are meant to be made (like: the engine may take advantage of type information available for the server's live properties) - maybe, for a comparison on other properties the datatype could be submitted with the query, for instance: <gt> <prop><foo:bar xsi:type="xs:integer" /></prop> <literal>1234</literal> </gt> - I think that querying into "structured" properties needs to be handled, especially considering the live properties introduced by ACL and deltaV. XPath still seems to be a good candidate for this. - Is there a server implementing Query schemata? Julian
Received on Wednesday, 13 June 2001 06:24:36 UTC