- From: Babich, Alan <ABabich@filenet.com>
- Date: Tue, 12 Jun 2001 13:13:58 -0700
- To: "'Julian Reschke'" <julian.reschke@gmx.de>, w3c-dist-auth@w3.org
(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 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 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 DASL said about data types is the following. First, you can have a query schema that describes the properties, including their 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. Alan Babich -----Original Message----- From: Julian Reschke [mailto:julian.reschke@gmx.de] Sent: Tuesday, June 12, 2001 3:12 AM To: w3c-dist-auth@w3.org Subject: Re: Moving DASL to Experimental Hi, I'm looking for other parties that would be interested on working on DASL again. With the current status of the spec I have mainly two problems, both of which apply to the basicsearch grammar: 1) The spec is completely silent about how the grammar engine is supposed to know about data types. For instance, I would suspect that property values for getcontentlength are supposed to be compared as numbers, while getlastmodified need a date comparison. 2) The grammar for accessing properties is not really XML-friendly, which has led to inventions like "DAV:iscollection". Indeed, this so-called "synthetic property" only solves one special case and leaves the rest (lockdiscovery, attributes, deltaV computed properties) untreated. I think DASL needs a grammar which can do "arbitrary" queries into the attributes, so something with the power of XPath would need to be used. In addition, I'm not happy with the language in chapter 3 (discovery of grammars). It mixes namespace prefixes with URI schemes, which is only correct in the very special case of "DAV:" (being a URI scheme and also the prefix used there). Julian
Received on Tuesday, 12 June 2001 16:14:38 UTC