Data Modeling Practice - Data Modeling Practice Practice...

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Components of an ERD (Review) Business Rules Information from the user’s business environment that governs how his data is used—for example, policies, procedures , constraints, regulations, formulas and calculations . Entity An object in the user’s business environment that he wants to track or keep up with –for example, customers, orders, employees, products, services . Attribute A data item that describes an entity—for example, employee ID, last name, date of hire, number in inventory . An IDENTIFIER --one or more attributes that uniquely identify one member of the entity. For example, Product_Number, Employee_ID, Order_Number. Identifiers are also called Primary Keys Relationship An association between entities—for example, customer places an order, player plays on a team. ..
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Tips and Guidelines for ERD Determining what data should be in the model can take practice and experience. Watch out for: User/Owner/Company name –don’t use these in the model! Model only the objects of interest to the company /owner/user. "Fluff" --background information that does not directly relate to problem at hand. Read for information, but don’t model it. Input/output —for example, reports. Resist the temptation to include these in the model as entities. Scope “Creep” –For class problems, diagram only the information given in the problem. Resist the temptation to add details to the original problem as stated. Processes –descriptions of “HOW” data is collected, stored, used or deleted. We are only interested in the data items for the purpose of the model. The processes will be documented in other ways.
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Steps in Data Modeling (Review) 1. Identify the entities.* 2. Determine the relationships between the entities. 3. Draw a draft ERD with entities and lines representing relationships connecting the entities. 4. Assign identifiers and attributes to the entities in the diagram. Identifiers are underlined to distinguish from other attributes. 5. Assign cardinality and modality symbols to relationship lines. ( Cardinality and modality are discussed in Data Modeling Part 2 .) For Many-to-many relationships, model the relationship using an associate entity. *If you are having difficulty determining the entities (step 1.), an alternative is to
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This note was uploaded on 09/21/2011 for the course CGS 2545C CGS 2545c taught by Professor L during the Summer '10 term at University of Central Florida.

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Data Modeling Practice - Data Modeling Practice Practice...

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