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Entity-Relationship (ER) model. Popular high-level conceptual data model. ER diagrams. Diagrammatic notation associated with the ER model. STEPS IN DATABASE DESIGN. Requirements collection and analysis. DB designers interview prospective DB users to understand and document data requirements. Data requirements.
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- Lecture 7
- Comprehensive
- Concise/High-level
- Algorithmically Transformable
- Set of entities that have the same attributes
- CAR
- DEPARTMENT
- PROJECT
- DEPT
- FACULTY
- STUDENT
- DEPT
- STUDENT
- DEPT
- is important)
- Tutee
- >N, can go to (1) entity
Context Design & Implementation Process Goals of Conceptual Design Entity-Relationship (ER) Model One ER Diagrammatic Notation Requirements Elicitation Approaches to Conceptual Design
Entity types, relationships, and constraints Sanity check of data & functional requirements Reference for [unit/integration] testing/analysis
Easy to understand technically Easy to communicate with non-technical users Facilitates focus on data (vs. storage/implementation details)
• Improves application development efficiency, reduces errors Entity • Thing in the real world Attribute Property of an entity Most of what we store in the database Relationship Association between sets of entities Possibly with attribute(s) Graphical depiction of an ER model Many notations, this class... All cars have a year, age, make, model, reg...
Make Year Model All cars have a year, make, and model.
Can be subdivided into smaller subparts All cars have a year, make, model, and registration. Can take a [possibly specified] number of values. All cars have a year, make, model, registration, and some number of colors. Make Year Model Color CAR Registration State Number The value uniquely identifies each entity All cars have a year, make, model, re...
Manager Manager_ Start_Date Draw an ERD for the following description: A department controls a number of projects, each of which has a unique name, a unique number, and a single location. Location Name Number
Controlling_ Department Draw an ERD for the following description: We store each employee’s name (first, last, MI), Social Security number (SSN), street address, salary, sex (gender), and birth date. An employee is assigned to one department, but may work on several projects, which are not necessarily controlled by the same department. We keep trac...
CHAIR_F All departments have a faculty member who serves as the chair. A faculty member can only chair one
department. Associates one or more sets of entities
All students must have a department in which they major.
CHAIR_F FACULTY Associates one or more sets of entities
MINOR_D Students may have any number of departments in which they minor.
CHAIR_F FACULTY Associates one or more sets of entities – One = recursive (role
MAJOR_D Constrains the number of entities that can participate in each role of the relationship Tutor
All departments have a faculty member who serves as the chair. A faculty member can only chair one department. Constrains the number of entities that can participate in each role of the relationship Constrains the number of entities that can participate in each role of the relationship Constrains the number of entities that can participate in each ...
N MAJOR_D STUDENT N MINOR_D Tutor N Tutee M TUTORS Each department chair has an office. Office
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Entity-Relationship Schema. Describes data requirements for a new information system. Direct, easy-to-understand graphical notation. Translates readily to relational schema for database design. But more abstract than relational schema. E.g. can represent an entity without knowing its properties. comparable to UML class diagrams. Entities:
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Contents. Basic concepts: entities and entity types, attributes and keys, relationships and relationship types Entity-Relationship schema (aka ER diagram) Constraints on relationship types Design choices Enhanced Entity-Relationship model features Steps in designing an ER schema Translation of an ER schema to tables.
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For example, in a titration in which you have been asked to calculate the concentration of an acid or base, the combined uncertainty values of the apparatus can be linked to the final result.
Feb 1, 1995 · The method used in this study is Entity Relationship Model or better known as ER Model. ER Model facilitates data storage where it can serve as the basis for databases that store problem...
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This is a supplement that explains the differences and shortcomings of some popular entity- relationship diagram (ERD) notations which you will or may already have encountered in your studies.
