DATA a Dictionary - in German translation also data item book, data catalog or somewhat in a diffuse way data catalog mentioned - is a catalog of meta data, which contains the definitions and representation rules of data elements. It describes all application data of an enterprise and the relations between the different data objects with the goal of a redundancy-free and central definition of the data structures and corresponds thus to a representation of the user-specific Datenmodells.Im context of a relational data base (DBMS) is DATA a Dictionary a quantity of tables and sighting, which are only read by the query language (e.g. SQL) (READ only). DATA the Dictionary is thereby again as a data base developed, contains however not directly the application data but meta data, i.e. data, which describe the structure (not contents) of the application data. Structure and care DATA of the Dictionary take place typically by means of an interactive care dialogue or with a data definition language (DDL).

Active, passive and integrated DATA Dictionaries

An active DATA Dictionary reflects at any time the current detailed conditions of the data model. Changes at the structure of a data base can take place directly in the care surface DATA of the Dictionary, or with other means, e.g. a command interpreter of a DDL. Independently like these changes, are always automatically ensured the topicality active DATA take place of a Dictionary.

In a Dictionary this is not given passive DATA. Changes at the structure of the DBMS must be updated in DATA the Dictionary (dd) manually, if that is desired and economically possible. In particular dd products for the modelling and documentation of the conceptional data model suffer from this problem.

Interfaces from DATA the Dictionary to humans and software

DATA a Dictionary can be consulted over the following interfaces [see also Elmasri, s.625]:

Distinction from DATA Dictionaries to modelling level

With respect to the development and care of data models different modelling levels are differentiated:

• Conceptional level (i.d.R referred to an area of application, in the economical informatics often also enterprise far or even enterprise-spreading.
• Logical level
• Physical level, in which the conceptional/logical data model is illustrated and converted related to a certain DBMS.

According to the different levels of the data modelling, the DATA Dictionaries can be differentiated according to support of these model levels. Depending upon level thereby the DATA Dictionaries differ after kind, contents and also data types of the necessary meta data, in addition, concerning their functions and evaluation possibilities.

DATA Dictionary to conceptional/the logical data modelling

To DATA the Dictionary to conceptional/the logical data modelling belong:

• Definition of the and data elements and their relations among themselves
• Economical definitions and explanations the same
• Reference and statement on the use in the physical data model

Apart from the definition substantial data objects and/or - elements and their relations, more typically also detailed describing texts on level of the respective are deposited, which are linked by means of hyperlink technology among themselves. If an organization develops a enterprise-far data model (UDM), to each and each data element information is gathered to application-oriented semantics, to the data type and for - representation. The semantic components focus in the illustration of the exact meaning of a data element and are formulated as flow text. The representation rules define like data elements in the computer to be stored (e.g. data type such as Integer, text, maximum text length, input format, Ausgabeformatte, etc.). This first form is not frequently in the function range of a DBMS system contained as built-in function. Therefore here often set off isolated solutions must be used. These represent however in the reference to the DBMS system a passive DATA Dictionary. Changes at the conceptional data model cannot be transferred automatically to the physical data model of the DBMS.

Under ISO/CInternational Electronical Commission 10027 (see below) specifications were compiled, which are to permit manufacturer and platform-spreading exchange of information resources between different DATA a Dictionaries.

DATA Dictionaries are specify as a glossary (terms and definitions) because its terms frequently still permits no conclusion on the data elements stipulated by the glossary. Datadictionaries to become to be able also the definition separately from data models (ERE diagrams, UML models) administers, however then again the problem of the integration and the Roundtrip actualization places itself. Complex data models develop on DATA a Dictionary, the various relations (relations) between the data elements finally in the form of tables are therefore naturally modelled nevertheless here and represented, what permits evaluations also table-supported in the following. Naturally thereby also graphic report analyses are possible e.g. in the form of ERE diagrams. Statement on the use and a hyper+left-like navigation by all data elements should support a reading of the data model. Datadictionaries can be developed further to complete Ontologien and/or classes and/or business processing concepts, if discrete logic is added to the data elements, which describe their transformation logic. Even if apart from the data structure the methods are described for data manipulation, one speaks of a Repository.

DATA Dictionary for physical data modelling

To DATA the Dictionary for physical data modelling belong:

• Exact technical definitions of the data fields and tables
• Physical definition of the primary and foreign key relations
• Integrity conditions
• User name, roles and authorizations
• Pattern objects
• Stored Procedures and of trigger
• Definition of the general data base structure, e.g. Speicherallokationen
• Test information

This form is present in each DBMS as active DATA Dictionary, is not visible however not in every case for the application programmer. Where such DATA Dictionary is not visible, it forms nevertheless the data base structure as data base schema, is however for hidden put down into system tables. With each access to the data base bank the DBMS system software reads the data base schema, in order to be able to recognize the structure and the memory place of the queried data.

Articles in category "DATA Dictionary"

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