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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Annotations in XPath-NG? (Re: XPath/XSLT 2.0 co
 This is actually something similar to what I intend to implement over an XML Repository [probably Xindice]. We have a requirement to be able to; given a node, find all annotations [of a particular type or matching certain criteria], on that node. While I want to be able to express this as an Axis in the XPath object model, I've got a few problems with that: 1. How do I specify the Annotation context for the annotation axis. Our annotations are stored as standoff annotations, and to complicate things further, may apply to either a single document or a collection of documents. 2. It's a heck of a lot easier to create a new XPath function in existing public domain XPath implementations than it is to change the parsing and execution model. 3. The association between a node and it's annotation isn't totally clear. Does a node have an annotation if the annotation directly specifies the node? That's easy -- yes. Does the node have an annotation if it's ancestor has an annotation? That's not very clear, although I lean towards yes. So, then I really want to axes, the annotation:: axis which returns the former, and the annotation-closure:: axis, which returns the latter. This became to complicated for what I required in the short run, so, I've made a design decision that we'll probably have to go the function route. What I came up with for an API was: node-set extension:annot(node-set source [, string tag]) Returns the node-set consisting of all annotations on source. If tag is supplied, then only those annotations whose element name matches it will be returned. The value of tag is a list of tags to be included in the result, separated by white space or | symbols [NOTE: What I really wanted to pass in to this function here was a relative location path so that I could optimize the selection]. So expr[extension:annot(.,"tag")] returns anly those nodes which have a <tag> annotation, and expr[extension:annot(./ancestor-or-self,"tag")] selects a similar set, save that the annotation can be on the nodes or its ancestors. I didn't feel it necessary to have a function that automatically applied the ancestor-or-self notion simply because the number of ancestors is going to be small [3-7] for any given node I have to apply this to in our system, however, I may change my mind once I start implementing. Of course, I still haven't figured out how to set the context up yet for annotations, but still I have a few weeks to do some more design. Keith Engineering is what happens when science and mathematics meet politics. Products are what happens when all three meet reality. -----Original Message----- From: Jeni Tennison [mailto:jeni@j...] Sent: Sunday, October 06, 2002 1:17 PM To: uche.ogbuji@f... Cc: Eric van der Vlist; xml-dev@l... Subject: Re: Annotations in XPath-NG? (Re: XPath/XSLT 2.0 concerns) Hi Uche, > My foirst comment is that it should be generic annotation, not just > type annotation. My thoughts would be: > > Add an "annotation" property to each node. This is a simple > key/value pair where the key is URI (or is that anathema ;-) ) and > the value is any XPath 1.0 object (which would even allow > annotations to be cross-node links). > > You can access any particular annotation for any particular XPath > object with a function lookup(annoitation-key). Of course, some > facilities, such as optimizers, might use annotations behind the > scenes, directly. > > Does this sound like a good general approach? Definitely. This is very close to what David Rosenborg and I were discussing at: http://lists.xml.org/archives/xml-dev/200210/msg00212.html and follow-ups. Personally I'd use qualified names rather than URIs for the "lookup", but that's because I envisage getting to annotation information through an axis rather than through a function and because QNames are easier to write than URIs. Perhaps a function: annotations(node) that returns a node set, and let the user use XPath mechanisms for doing the lookup within that node set? Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/ ----------------------------------------------------------------- The xml-dev list is sponsored by XML.org <http://www.xml.org>, an initiative of OASIS <http://www.oasis-open.org> The list archives are at http://lists.xml.org/archives/xml-dev/ To subscribe or unsubscribe from this list use the subscription manager: <http://lists.xml.org/ob/adm.pl> 
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