also sprach martin f krafft <[EMAIL PROTECTED]> [2003.02.17.0930 +0100]: > only looking for specific features that differ, but also (and more)
e.g.: ORDER: records are unordered in the relational model, but ordered in the other two. INHERENT CONSTRAINTS: records cannot exist without a parent/relating record in the hiearchical model due to the structure. the existence of unrelated records in the relational and network model can be controlled by the data-definition language and/or the design of the various record types. RELATIONSHIPS: in the hierarchical model, a record must have one and only one record from which it is deviated. in the network model, there can also only be one parent record (but there doesn't have to be). in the relational model, such constraints don't exist. (this all means jack when working with "virtual parents") CASCADING: a deletion of a "parent" record automatically removes children in the hierarchical model. the same *can* be true for the relational and the network model (not sure about the latter), but it has to be configured in the DDL, i.e. it's not inherent. CURRENCY: operations in the relational model always start from the "global" position whereas there is a position pointer maintained in the DBMS in the other two models. Operations in the hierarchical and network models are mostly relative to that position pointer. -- Please do not CC me when replying to lists; I read them! .''`. martin f. krafft <[EMAIL PROTECTED]> : :' : proud Debian developer, admin, and user `. `'` `- Debian - when you have better things to do than fixing a system NOTE: The pgp.net keyservers and their mirrors are broken! Get my key here: http://people.debian.org/~madduck/gpg/330c4a75.asc
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