- From: ALEXANDRU,MARIUS (HP-Romania,ex1) <marius_alexandru@hp.com>
- Date: Fri, 6 Oct 2000 16:27:57 +0200
- To: fallside@us.ibm.com
- Cc: www-xml-schema-comments@w3.org
Hi, I apologize for this mail but I want to present you a strong limitation of Schema model comparing with the entity-relationship model that maybe could be considered at your meetings regarding the xml-schema draft. Suppose that you have to entities : <entity name="a" id="a"> ... </entity> <entity name="b" id="b"> ... </entity> and a relationship Rab(a,b) between the two entities : <relation name="Rab"> <role name="has-a" occurs="0,n"/> <entity idref="a"/> </role> <role name="has-b" occurs="0,n"/> <entity idref="b"/> </role> </relation> In my opinion, the E-R model (I don't used an exact formalism to describe it in the above example) can allow us to produce the following valid XML productions: Valid Production 1: <a> <Rab> <!-- we have to include also the rolename here too--> <b> ... </b> <b> ... </b> <b> ... </b> </Rab> </a> Valid Production 2: <b> <Rab> <!-- we have to include also the rolename here too--> <a> ... </a> <a> ... </a> <a> ... </a> </Rab> </b> Valid Production 3: <Rab> <!-- we have to include also the rolename --> <a> ... </a> <b> ... </b> </Rab> <!-- or another description that allow us to introduce more couples on a single <Rab>...</Rab> chunk. So as you can see the XML Schema definition (at www.w3.org) don't allow us to produce all the productions that the E-R model could provide. In fact the problem is more important that this : the tree (xml) structure its in itself a very constraintfull syntax (so a lot of patterns have to be specified (like the already existing : sequence,conjuction,disjunction etc..) in order to give more flexibility of this strong syntax. Also, I cannot imagine a good XML-Query definition that will depend so strongly on the Syntax in which the data are presented. I also think that this limitation will affect the IT industry for a long period of time since now (please take this last sentence not so serious as it seems, but in any case is my opinion) Thanks for your time and Best regards, Marius
Received on Friday, 6 October 2000 10:28:16 UTC