[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Access Languages are Tied to Schemas
Jonathan Robie <jwrobie@m...> wrote > The following properties of object models are easily represented in > SGML/XML: > o Identity > o State > o Type I would disagree that even these items can be easily represented in SGML/XML (for example, State is more complicated than a particular set of attribute values). I think it is more the other way around: SGML/XML has a particular model of Identity, State, and Type which an object model can easily represent. But in any case, these items are (mostly) the core concept of OO (i.e. Objects) instead of being properties of object models. Objects have Identity, State, and Behavior where the implementation of both state and behavior is encapsulated. Object models describe the possible objects and structures that can exist in a system. This will include describing[1]: Types: The interfaces (methods, associations, and abstract state) that objects can have. Associations: The possible relationships between objects Operations: The messages an object can respond to State Models: The possible state transitions for an object Attributes: The simple associations (to basic value types) of an object Inheritance: The similarities/relationships among types DTDs can describe some of this modeling information, but not particularly well and really only for a limited set of object models. Examples of weaknesses are: only one true association (content) which is a pure containment, all other attributes must be basic data types, limited cardinality control, likelihood of arbitrary ordering, inability (or difficulty) to express Type relationships, inability (or difficulty) for an Object to support more than one type. These are weaknesses compared to the most basic modeling abilities of common modeling techniques (UML, Booch, HOOD, Syntropy, OORAM). Thought about another way, DTDs are good models for textual input of information (what rules must be satisfied by the encoding) but this should be considered only a view onto the true information model. SGML/XML describes a construction view of an information model and provides the front-end to instantiating an Objectbase from that model. Using SGML/XML to try to describe any information model (via DTDs) will be over extending its abilities into areas where other tools/techniques are much better qualified. --Mark mark.fussell@c... [1] An implementation of an object model (or an implementation model developed from a conceptual model) also uses classes, methods, and instance variables to satisfy the above descriptions within a particular system. I am trying to use the most established and main-stream definitions of all these terms, but you may also want to see the references at the MONDO site for possible different definitions (e.g. Dictionary of Object Technology [Fireside+E 95]). i ChiMu Corporation Architectures for Information h M info@c... Object-Oriented Information Systems C u www.chimu.com Architecture, Frameworks, and Mentoring xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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