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4.12 Elementary Method "E/R Modeling" (ER)  

  4.12 Elementarmethode "E/R-Modellierung" (ER)

Contents  
  • 1 Identification/Definition of the Method
  • 2 Brief Characteristic of the Method
  • 3 Limits of the Methods Application
  • 4 Specification of the Methods Allocation
  • 5 Interfaces
  • 6 Further Literature
  • 7 Functional Tool Requirements

    • 1 Identification/Definition of the Method

    /Wiborny, 1991/ chap. 3.3

    2 Brief Characteristic of the Method

    Objective and Purpose

    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:

    Operational Sequence

    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.

    Recommendation

    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.

    1. Analysis and description of the relevant entity types
    2. Analysis and description of identifying attributes
    3. Analysis and description of the relevant relationship types
    4. Checking the present preliminary data model with the concerned operating departments and a first comparison with the preliminary functional model
    5. Adjusting the data model (correction of inconsistencies and redundancies of relationship types, possibly resolution of N:M relationships)
    6. Analysis, description, and allocation of attributes to entities
    7. Analysis and description of integrity conditions
    8. Checking the detailed data model, adjusting it with the detailed functional model
    Further descriptions of the operational sequence can be found in the literature mentioned under 6.

    3 Limits of the Methods Application

    In applications with more than twenty entities, E/R Modeling generally requires a tool for the collection of the special E/R model specifications. Only then it is possible to document efficiently the specifications, additions, improvements, and modifications of the E/R model.

    4 Specification of the Methods Allocation

    No. Activity Description
    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.

    5 Interfaces

    No. Interface Observation Information in Annex 1
    5.1 ER-DFM 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).

    Note:
    In case of large models (ER und DFM - Data Flow Modeling) the allocation is only practicable by means of tool support.

    		4.3 Interface DFM-ER
    5.2 ER-DNAV 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.

    Recommendation:
    It is recommended to normalize the E/R models prior to the application of DNAV - Data Navigation Modeling.

    		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

    6 Literature

    /Batini, 1992/ Conceptual Database Design
    /Martin, 1990a/ Information Engineering, Book II
    /Müller-Ettrich, 1989/ Effektives Datendesign
    /Münzenberger, 1989/ Eine pragmatische Vorgehensweise zur Datenmodellierung
    /Vetter, 1990/ Aufbau betrieblicher Informationssysteme
    /Wiborny, 1991/ Datenmodellierung, CASE, Datenmanagement

    7 Functional Tool Requirements

    SSD09 - Supporting Information Structuring

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