XML Data Model?

Discussion in 'XML' started by Irfan Bondre, Jul 20, 2005.

  1. Irfan Bondre

    Irfan Bondre Guest

    What is Data Model?

    What is XML Data Model?
    Any spec for XML Data Model?

    What is XML info Set?


    Irfan
    Irfan Bondre, Jul 20, 2005
    #1
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  2. Irfan Bondre

    Andy Dingley Guest

    On 19 Jul 2005 22:54:48 -0700, "Irfan Bondre" <> wrote:

    >What is Data Model?


    A "data model" is an abstract notion, which a document might represent.
    This data model describes the entities (things) that can be represented
    by it, their properties (values or constraints that can be attached to
    them) and their inter-relationships.

    A data model can also have a "serialisation", a notation for how to
    write down its content as a stream of characters, such as can be stored
    in a file.

    >What is XML Data Model?


    There isn't one. See below.

    >Any spec for XML Data Model?


    See above.

    >What is XML info Set?


    http://www.w3.org/TR/2004/REC-xml-infoset-20040204/

    The XML recommendation was written without a data model, as just a
    serialisation. It was later realised that a formal data model would be
    useful and so info-set was written to describe a concensus about the
    pre-existing situaton.

    SGML doesn't have a data model. It only has a serialisation. If an SGML
    application wants to interpret this as a data model, then it must invent
    its own. Obviously this limits inter-operability between applications.

    XML's implicit data model is well-defined, but not deeply so. It has
    many limitations.

    RDF takes the other direction to SGML and had a data model first and
    foremost, together with a number of alternative serialisations. One is
    RDF+XML, the next most popular is as Triples. Because there is a
    well-defined data model it's relatively easy to add new serialisations,
    should you wish.

    Because RDF took the data model question first, it also has a far more
    capable data model than plain XML. It may represent a graph, rather than
    just a tree (a branching tree is a subset of a generalised graph).
    Secondly it allows entities to be stored in either the document, or
    external to it, through a well-defined addressing mechanism. XML can
    only use entities within the current document.

    If you want details as to what XML's data model is, rather than what a
    data model is for, then read Infoset in detail. The RDF data model may
    also illuminate some of its limitations.
    Andy Dingley, Jul 25, 2005
    #2
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  3. Irfan Bondre

    Stefan Ram Guest

    Andy Dingley <> writes regarding RDF:
    >capable data model than plain XML. It may represent a graph, rather than
    >just a tree (a branching tree is a subset of a generalised graph).


    In XML, graphs might be expressed using attribute
    values of type ID and IDREF.
    Stefan Ram, Jul 25, 2005
    #3
  4. Irfan Bondre

    Irfan Bondre Guest

    Does that mean, XML when initialy written only empahized in terms of
    every tags must have a open and close tags, attributes values should be
    quoted, no duplicate attributes within the same tag etc..

    i.e the above represented the data model or "serialization" model....

    And Later came the XML Info set which implied in terms of elements,
    document node, attributes and their relation ship.
    Irfan Bondre, Jul 26, 2005
    #4
  5. Irfan Bondre

    Andy Dingley Guest

    On 25 Jul 2005 22:51:21 GMT, -berlin.de (Stefan Ram) wrote:

    > In XML, graphs might be expressed using attribute
    > values of type ID and IDREF.


    Have you ever seen this successfully done ?

    Yes, XML has this feature. In practice though it just doesn't work well
    enough to be useful.

    Perhaps the biggest limit though is XML's dependence on "the graph"
    being contained entirely within a single document. ID and IDREF fall
    apart very badly when you get beyond this stage.
    Andy Dingley, Jul 27, 2005
    #5
  6. Irfan Bondre

    Andy Dingley Guest

    On 25 Jul 2005 18:13:10 -0700, "Irfan Bondre" <> wrote:

    >And Later came the XML Info set


    Yes. XML appeared around 1997, Infoset was 2000, AFAIR (I worked with
    one of the authors). This was after RDF had become of great interest to
    our group and it was the difference between the two platforms that
    inspired much of the Infoset work (or at least the inspiration to do
    it).
    Andy Dingley, Jul 27, 2005
    #6
  7. Irfan Bondre

    Stefan Ram Guest

    Andy Dingley <> writes:
    >>In XML, graphs might be expressed using attribute
    >>values of type ID and IDREF.

    >Have you ever seen this successfully done ?


    ID and IDREF are used in the XHTML-1.1 DTD

    http://validator.w3.org/sgml-lib/REC-xhtml11-20010531/xhtml11-flat.dtd

    several times. For example, to describe the relation between
    the for-attribute of a label-element, which must match the ID
    of a control.

    The HTML 4.01 specification say:

    The for attribute associates a label with another control
    explicitly: the value of the for attribute must be the
    same as the value of the id attribute of the associated
    control element. More than one LABEL may be associated
    with the same control by creating multiple references via
    the for attribute.

    The label elements, control elements and this association form
    a graph. I assume, this is successfully used in the world wide
    web. (Because I am not aware of a search engine that is
    indexing these parts of the source code, I can not give
    statistics of the amount of use.)
    Stefan Ram, Jul 27, 2005
    #7
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