Ch7New1-11 - Chapter 7, Part 1: Conceptual Data Modeling...

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Unformatted text preview: Chapter 7, Part 1: Conceptual Data Modeling Conceptual D. Harrison McKnight Eli Broad College Eli of Business of Essential 2 Know Essential From a written scenario, be able to From correctly draw an ER model, displaying: correctly – Entity types – Relationships – Relationship labels – Attributes (including identifiers) – Subtype-supertypes – Cardinality-Optionality Key terms Conceptual Data Modeling: A Rationale Rationale Data modeling dates to 1974; late Data 1980s in practice 1980s Essential for referential integrity of Essential database database ER modeling is an intellectual skill DFD and ER: Must-know techniques Views of a System Views Data What are the relevant locations and how is communication between them handled? Network Process People What activities are performed, and how? Who are the stakeholders and what roles d they fill? Data View Data What “things” are important & how are they related to each other? Modeling Tools: Entity­Relationship Diagram Data Process Data Dictionary Network People Data Boundaries / Interaction Data What data is used in what processes? Where is data located & how is it shared? Data Process Network People Who uses what data? Business Situation Enterprise Data Model Business Area Data Model Conceptual Data Model Normalized Data Model Physical Data Model Implemented Database Business Situation Enterprise Data Model Business Problem Focus Technology Solution Focus Business Area Data Model Conceptual Data Model Normalized Data Model Physical Data Model Implemented Database Data Modeling in Analysis Data What are the objects (“things”) in this domain? What are the attributes or characteristics that describe What the things? the How are the things related to each other? What business events cause these objects to be What created, eliminated, or changed? created, Do these objects have a history? What business rules or policies impact the creation, What elimination, modification of these objects? elimination, Data Modeling in Analysis Data Entity-Relationship Model – Peter Chen, 1970s – “Translate” English sentences into graphical Translate” representation of entities, relationships, and attributes attributes Variations & Extensions to ER Models – Generalization/specialization structures Generalization/specialization (Supertype/Subtype) (Supertype/Subtype) – Complex relationships & constraints Entity-Relationship Entity-Relationship Modeling Concepts Basics Entity – Type – Instance Relationship – – Cardinality Ordinality Attribute – Identifier Advanced Supertype/Subtype Supertype/Subtype Relationship Relationship Recursive Recursive Relationship Relationship Ternary Ternary Relationship Relationship ER Modeling ER Course has A COURSE has zero­to­many SECTIONs. A SECTION is for one­and­only­one COURSE. A SECTION is taken by zero­to­many STUDENTs. is for Section A STUDENT takes zero­to­many SECTIONs. is taken by Student takes ER Modeling ER Course has Optionality of 1 = Mandatory (Always) participation in the relationship. A SECTION has to be associated with at most one COURSE. A SECTION is always for at most one COURSE. is for Section is taken by Student takes ER Modeling ER Course has Optionality of 0 = Optional (Sometimes) participation in the relationship. A COURSE may or may not be associated with a SECTION. A COURSE sometimes has a SECTION. is for Section is taken by Student takes ER Modeling ER Course has Cardinality of 1 = Maximum participation in the relationship is 1. A SECTION must be associated with at most one SECTION. is for Section is taken by Student takes ER Modeling ER Course has is for Section Cardinality of Many = Maximum participation in the relationship is many (one or more). A COURSE may be associatedwith one or more SECTIONs. A COURSE may have many SECTIONs. is taken by Student takes Selecting an Identifier from Selecting among Candidate Keys among Employee ssn first name last name work phone type 111­11­1111 222­22­2222 333­33­3333 444­44­4444 ... Mary John Mary Barry Smith Doe Jones Smith 644­1234 644­9876 644­7866 644­6722 faculty instructor staff faculty Some Rules of Thumb Some General – – – Group things together that logically belong together. Group logically Represent each fact once and only once. Entities are usually tangible things, events, roles, or Entities usually locations (noun-ish). locations – Relationships are often activities or events (verb-ish). Relationships often Entities versus Attributes – It’s not an entity if it has only one attribute or only one It’s instance. – If you don’t want to store several items of data about If it, it’s probably not an entity—more likely an attribute. it, More Rules of Thumb More Attributes and Identifiers – An entity can have more than one attribute as An an identifier (composite identifier). – Identifiers cannot be changed; cannot be null. To Use Subtype-Supertype or not – Use subtype-supertype if subtypes have unique Use attributes or participate in unique relationships. attributes Essential 2 Know Essential From a written scenario, be able to From correctly draw an ER model, displaying: correctly – Entity types – Relationships – Relationship labels – Attributes (including identifiers) – Subtype-supertypes – Cardinality-Optionality Key terms ...
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