Closed mbjones closed 7 years ago
mbjones
commented
7 years ago Original Redmine Comment Author Name: Peter McCartney (Peter McCartney) Original Date: 2002-09-10T17:20:21Z
I think this is also the reason why we're having problems with Stylus Studio which is based on xerces. It reports a flood of errors related to key statements.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Matt Jones (Matt Jones) Original Date: 2002-09-11T18:51:59Z
OK, here's the deal as far as I can tell with the key validity problems. These surfaced when we upgraded Xerces, which became more sensitive to these schema validity problems. When you define a key, you define a set of nodes to be checked using the "selector" xpath expression. This produces a node set, and for each field in that node set, it checks that the "field" selector contains a unique value AND is not nil.
This means two things for us: 1) id attributes can not be optional, because we have to have a value to pass the validation test 2) our selectors can't look at every node (as they currently do by using something like ".//*"), because such a broad selector will return nodes that don't allow the id attribute, and thus would not have a value for the key
The only solution that I can see right now is: 1) change all id attributes from optional to required 2) change our xpath selectors to only select eml fields that contain an id attribute
This is a pretty major change, but as it stands now the key/keyref stuff prevents us from ever creating a valid document. Comments appreciated.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Chad Berkley (Chad Berkley) Original Date: 2002-09-11T19:23:01Z
I think the solution you propose sounds simple enough. I don't see required id fields as being a big issue, although I know it has been an issue with others before. The xpath selection seems trivial. We definitely need this stuff to validate correctly with existing tools or we may have a mess on our hands.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Peter McCartney (Peter McCartney) Original Date: 2002-09-12T23:19:44Z
needless to say, im one of the ones that is not wild about id's being required. when we agreed on the identifier/reference thing, it was with the understanding that one could produce an eml with duplicated content or choose to use identifiers.
I think eml should be about content, not schemas. to me, all this keyref stuff is about enforcing one opinion on the mangement of similar information within one document - it has nothing to do with content standards. If we're facing a problem caused by key refs that is going to force everyone to have to create documents following this narrower opinion, I would sooner leave them optional and let external software do the enforcing. In order to used them effectively, youre dependent on software to manage them anyways.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Tim Bergsma (Tim Bergsma) Original Date: 2002-09-13T12:59:11Z
Now I'm scared. I've been largely ignoring the identifier discussion, probably because I thought they wouldn't affect me. When triples were dropped, I suddenly felt that I might be able to generate eml independently, without expert intervention. Peter's comments about identifiers are unsettling. I'm sure we'll get it figured out, but at what cost, on a site basis? I'll be paying more attention now.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Chad Berkley (Chad Berkley) Original Date: 2002-09-13T14:23:08Z
Alas, all is not lost! Matt and I spent a bunch of time yesterday tracking down exactly what was going wrong with the keys. We feel pretty strongly that this is a bug in xerces and that we are doing it correctly. Matt entered a bug in the xerces bugzilla: http://nagoya.apache.org/bugzilla/show_bug.cgi?id=12592 If you look at it, you can see what we figured out as well as some sample documents that illustrate our points.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Matt Jones (Matt Jones) Original Date: 2002-09-13T22:54:07Z
Actually, the crux of the issue still remains in that xerces seems to be properly throwing an error if elements that particpate in a key are missing an id. The seem to be saying that all keys have the "NOT NULL" property. Bummer. It means there is nothing like the "ID" type from XML 1.0 in XML Schema. And this is why id would need to be required. I'm not at all satisfied with the "leave it optional and let people submit invalid docs", because that will never work. So...I think we need to continue this duscussion post RC1. In the meantime, I've commented out the key and keyref elements from eml.xsd so that everything validates. I'll update the README to indicate this is an outstanding problem.
The xerces folks are working on the othe rhalf of the problem, but its less critical as there would be a work-around.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Matt Jones (Matt Jones) Original Date: 2002-10-04T17:43:28Z
OK, so here's the deal. We've agreed ID should not be required. So that rules out using XML Schema keys to force uniqueness of the ids, because they do not allow nulls (if you select an element for a uniqieness check, its an error if it doesn't have the id at all). So...Chad wrote an EMLParser in Java that does the checks they way we want them done. It basically takes the key/keyref defs and validates that they follow the rules laid out in the eml spec. This code is shipping with the EML release, and has been exposed as a servlet on the web for people to use for validating their eml instances.
Hopefully Xerces will fix their bug, but the more serious problem would still remain, so our custom parser seems like the best solution for now. Will need to flag this in the distribution.
RESOLVED FIXED.
mbjones
commented
7 years ago Original Redmine Comment Author Name: Redmine Admin (Redmine Admin) Original Date: 2013-03-27T21:14:43Z
Original Bugzilla ID was 586
Author Name: Matt Jones (Matt Jones) Original Redmine Issue: 586, https://projects.ecoinformatics.org/ecoinfo/issues/586 Original Date: 2002-09-10 Original Assignee: Matt Jones
The new xerces reports a validation error for the "eml" module using ant test. This seems to be because keys are defined that are not used. Nedd to determine if this is truly invalid or a xerces bug. If its invalid, we'll need to change our key system becuase it won't work with optional key fields.