|4.12 Elementary Method "E/R Modeling" (ER)|
Within the scope of a defined task, a data model is set up in the Entity Relationship Modeling (E/R Modeling -ER) which is generally oriented on the special situation of the user and not on the DP realization. It is the aim of the E/R modeling to describe all those objects that are represented by data in an information system together with their corresponding relationships.
Means of Representation
The E/R diagram is used by the E/R Modeling as a means of representation. In practice, various notations are applied (also see /Wiborny, 1991/ pp. 56-112). The specification of a certain notation is realized within the scope of the operationalization. E/R diagrams must be comprised of the following features at least:
The generation of an E/R model is realized in a top-down procedure where more detailed and improved structures are created during each design step.
The following steps of a top-down procedure can be applied in a great number of E/R modelings for information systems. For a detailed description see /Münzenberger, 1989/ pp. 32-75.
|4.1||SD1.1 - Recording of Actual Status and Analysis||
Within the scope of the system actual recording/analysis for information systems, E/R modeling must be realized for the special user-oriented part with the same attention to detail and completeness as required for the more function-oriented part of the system actual recording/analysis. However, at least one E/R model with entity types, relationship types, and key attributes has to be generated for information systems.
The method thus covers at least the generation of a minimal E/R model of the data structure to be analyzed in subproduct User Requirements.Actual Status and Current Analysis.
|4.2||SD1.5 - User-Level System Structure||With regard to the data-oriented special requirements for information systems, a complete E/R model with all entity types, relationship types, attributes, and integrity conditions as well as the corresponding quantity structure must be attempted. The method covers the generation of the E/R submodels in subproduct User Requirements.Description of the Functionality with regard to the data to be processed by the functions on system level.|
|4.3||SD2.4 - Allocation of User Requirements||
Relevant E/R (sub) models have to be allocated to the subsystems and/or segments. In this connection modifications of the E/R models might become necessary.
The method covers possibly required modifications of E/R models for the data structures with regard to the subsystems and/or segments in subproduct System Architecture.Requirements Allocation.
|4.4||SD3.3 - Definition of Requirements for the Functionality||
For information systems, the data requirements defined on a professional level have to be stated more precisely and detailed from a technical point of view.
The method completely covers the generation of the E/R submodels in subproduct "Internal Information". The method covers the complete generation of the E/R model including the integrity conditions in connection with ELH - Entity Life History in subproduct Technical Requirements.Overall Function of Element.
|No.||Interface||Observation||Information in Annex 1|
The data flow diagram must be generated by means of reciprocal adjustments with the E/R Modeling (allocation of E/R submodels to the elements of the data flow diagram).
|4.3 Interface DFM-ER|
DNAV - Data Navigation Modeling is based on E/R models. Data navigation diagrams are generated by means of overlapping E/R diagrams with qualified and quantified access paths.
|4.6 Interface DNAV-ER|
|5.3||ER-ELH||ELH - Entity Life History requires E/R models and analyzes the life cycle of the included entities.||4.9 Interface ELH-ER|
|5.4||ER-FCTD||The functional hierarchy in FCTD - Functional Decomposition must be generated by interacting with the E/R Modeling (allocation of E/R submodels to the functions in FCTD - Functional Decomposition).|
|5.5||ER-LOGM||The complete E/R model is the starting point for the logical DB modeling. In this connection the (normalized) E/R models are transformed into DBMS-oriented data structures.||4.11 Interface ER-LOGM|
|5.6||ER-NORM||Within the scope of the E/R modeling, the normalization is applied to change an E/R model comprising attributes into a normalized form.||4.12 Interface ER-NORM|
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