![]() ![]() If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher level relational language (multiple-records-at-a-time). ![]() Users should always get the impression that the data is located at one site only. The end-user must not be able to see that the data is distributed over various locations. Integrity constraints specific to a particular relational database must be definable in the relational data sublanguage and storable in the catalogue, not in the application programs. The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update and deletion of data.Īpplication programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.Īpplication programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit unimpairment are made to the base tables. Rule 7: Possible for high-level insert, update and delete.Transaction boundaries (begin, commit and rollback)Īll views that are theoretically updatable are also updatable by the system.Data manipulation (interactive and by a program).However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and that is comprehensive in supporting all of the following items: Rule 5: The comprehensive data sublanguage ruleĪ relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). ![]() The database description is represented at the logical level in the same way as ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |