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    Entity Relationship Diagram: A Practical Guide: Erds Are Particularly Useful Where The Ba Wants To

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    Marvin Bucsit
    An entity relationship diagram (ERD) is a conceptual modeling tool that represents real-world data in the form of entities and relationships. Entities are things that need to have data stored about them, like customers or orders. Relationships show how entities are connected, like a customer placing multiple orders. ERDs are useful for database design, sharing information on stored data types, and revealing ambiguities or missing data items.

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    Entity Relationship Diagram: A Practical Guide: Erds Are Particularly Useful Where The Ba Wants To

    Uploaded by

    Marvin Bucsit
    30 views2 pages
    An entity relationship diagram (ERD) is a conceptual modeling tool that represents real-world data in the form of entities and relationships. Entities are things that need to have data stored about them, like customers or orders. Relationships show how entities are connected, like a customer placing multiple orders. ERDs are useful for database design, sharing information on stored data types, and revealing ambiguities or missing data items.

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    ERD Modelling-steps.docx

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    An entity relationship diagram (ERD) is a conceptual modeling tool that represents real-world data in the form of entities and relationships. Entities are things that need to have data stored about them, like customers or orders. Relationships show how entities are connected, like a customer placing multiple orders. ERDs are useful for database design, sharing information on stored data types, and revealing ambiguities or missing data items.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    30 views2 pages

    Entity Relationship Diagram: A Practical Guide: Erds Are Particularly Useful Where The Ba Wants To

    Uploaded by

    Marvin Bucsit
    An entity relationship diagram (ERD) is a conceptual modeling tool that represents real-world data in the form of entities and relationships. Entities are things that need to have data stored about them, like customers or orders. Relationships show how entities are connected, like a customer placing multiple orders. ERDs are useful for database design, sharing information on stored data types, and revealing ambiguities or missing data items.

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    © All Rights Reserved
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    Entity Relationship Diagram: A Practical Guide

    Peter Chen proposed the ERD in 1976 as a conceptual modelling tool which represents real world

    data in the form of entities and relationships - its primary application is in the design of relational

    databases; this is why it is also referred to as a Database Model.

    So, what exactly are entities and why would you want to draw one?

    Entities are things we need to store data about. Think of the user/business environment as a

    collection of “things” we need to know about. ERDs show entities, their attributes (qualities that

    describe entities) and the relationships amongst these entities.

    Though analysts mostly employ the use of ERDs for communicating the design of databases to

    developers, they are also an interesting way of illustrating the constraints that guide the use of a

    system to users through cardinality. For example, an ERD can show how many orders a customer

    can have or whether one order can only be linked to only one or multiple customers. Because it

    shows the relationship between the entities in the system, it may also be used for explaining

    constraints or business rules. 

    Data entities are represented by rectangles; relationships are represented by diamonds while

    attributes are represented by ovals (See example below).

    ERDs are particularly useful where the BA wants to:

     Model the data in an organization in terms of the different types/categories of data and their

    relationships to each other

     Share information on the types of data the organization stores

     Provide a model for database design

     Reveal ambiguities and other data items that the system needs to store
    In order to draw an ERD effectively, the BA must understand the domain and how things work –

    especially the business rules. 

    Take a look at this scenario:

    Customers visit the Centage website in order to purchase gardening items.


    Customers may or may not place orders at any one time. Each order is
    assigned a unique order code and an order may comprise multiple items.
    One order can have multiple transactions since customers may add items,
    change the quantity of items or even return items after purchase, if they so
    desire. Relevant customer information includes name, address and
    telephone number.

    The steps to creating an ERD are as follows:

     Identify the entities - Entities are easy to recognize as they are represented by nouns.

     Identify attributes - these are qualities/values associated with entities

     Identify the relationships between the entities  - relationships are identified by verbs

     Link entities to attributes and link entities together via their relationships

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