Database Design Conceptual Database Design Lecture 3 Lecture

Database Design Conceptual Database Design – Lecture 3

Lecture Objectives n Conceptual Database Design 2

Conceptual Database Design n Create the conceptual model n n A model which is the result of conceptual design Model will show the following: n n Entity – something about which someone wants to store data; typically a person, a place, a thing, a concept, or an event Attribute – a characteristic of an entity. It has a name and a data type 3

Conceptual Database Design n Model will show the following: n Relationship – an associate between entities. Has multiplicity (1: 1, 1: M, M: N) 4

Discovering Entities n n n Generally, nouns translate into entities Verbs translate into relationships among entities Relationships are bi-directional 5

Discovering Attributes n n Will be discovered when identifying entities They will describe an entity 6

Identifying Primary Keys n n If an existing attribute seems like a good candidate for the Primary Key, use it; otherwise create a new attribute PK is an attribute (or a combination of attributes) that will uniquely identify any given entity 7

Discovering Relationships n n n Verbs translate into relationships among entities Relationships are bi-directional Need to know the following: n n Optionality Cardinality 8

The Entity Relationship Model n n n Widely accepted and adapted graphical tool for data modeling Introduced by Chen in 1976 Graphical representation of entities and their relationships in a database structure 9

The Entity Relationship Model 10

The Entity Relationship Model 11

In Summary n Steps to create a conceptual model n n n Identify entities and attributes Identify primary keys Identify relationships between entities taking into consideration the business rules 12

Discovering Business Rules n n Constrain some part of the business For example: n n n An employee can only choose one benefit plan An employee may or may not have dependents An employee may opt out of a benefit 13

Discovering Business Rules n Sources of Business Rules: n n n Company managers Policy makers Department managers Written documentation n Procedures n Standards n Operations manuals Direct interviews with end users 14

Create an ERD for the following: n n n A department employs many employees, but each employee is employed by one department. A division operates many departments, but each department is operated by one division. An employee may be assigned to many projects, and a project may have many employees assigned to it. 15

Create an ERD for the following: n n Identify the entities, attributes and primary keys Draw the ERD showing relationships A Librarian wishes to make inquiries about borrowing activity within a library. The librarian can inquire about specific books borrowed by a customer using either their account or name. An inquiry can also be made by book category (such as fantasy, children’s, reference, etc) or an inquiry can be made that will look at the titles of a specific book. 16

Discovering Business Rules n n Identify the entities, attributes and primary keys Draw the ERD showing relationships Multiple Real Estate Listing Service (MRELS) is a company that has offices throughout Southern Ontario. These offices have a number of Real Estate agents working for them. MRELS deals in both residential and commercial real estate. Agents work with customers to get a listing or to find a listing for a customer. A listing will include the address and the type of property (residential or commercial), square footage, annual taxes and closing date. If it is a residential property, it will include number of bedrooms, number of bathrooms, special features (central air, heated by gas or oil, radiators or forced air, for instance). For a commercial property, it will include number of offices as well as number of docking bays (where trucks back up to be loaded/unloaded). 17