© M.E. Fayad 2002-2005 SJSU -- CmpE L8-2-S1 Misc Topics

Database Design

Dr. M.E. Fayad, Professor

Computer Engineering Department, Room #283I

College of Engineering

San José State University

One Washington Square

San José, CA 95192-0180

http://www.engr.sjsu.edu/~fayad

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S2 Misc Topics

2

Lesson 08-2:Misc. Topics in DB

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S3 Misc Topics

Lesson Objectives

Objectives

3

Understand DB Terminology Explain Relation Properties Understand how to Identify Candidate,

Primary, Alternate, and Foreign KeysUnderstand Entity Integrity and Referential Integrity

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S4 Misc Topics

External Level

View Level -- Users’ views of the db.

Conceptual Level

Logical View & Constraints View

Internal Level

Physical View or Computer’s view of the db. 4

Terminology: ANSI-SPARC Database Architecture

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S5 Misc Topics

A Relation is a table with columns & Rows.

An attribute is a named column of a relation.

A domain is the set of allowable values for one or more attributes.

A tuple is a row of a relation.

The degree of a relation is the number of attributes it contains. 5

More Terminology

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S6 Misc Topics

6

ExampleBranch

branchNo street city postCode

B005 22 Deer Rd London SW1 4EH

B007 22 Post St Aberdeen AB2 3SU

B003 22 S. Main St Glasgow GI1 9QX

B004 22 Mo Ave Bristol BS9 1NX

B002 56 Clover Dr London NW5 6EU

staffNo branchNo

B005B007B003B004B005

Staff Primary Key Foreign Key

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S7 Misc Topics

A Relation Schema – A named relation defined by a set of attribute and domain name pairs where:

R (A1:d1, A2:d2, …., An:dn)

A Database Schema – A set of relation schema each with a distinct name.

R = (R1, R2, ….., Rn)

7

More Terminology

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S8 Misc Topics

A relation has a name that is distinct from all other relation names within the same db.

Each cell of the relation contains exactly one atomic (single) value.

Each attribute has a distinct name.

The values of an attribute are all from the same domain.

8

Properties of Relations (1)

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S9 Misc Topics

Each tuple is distinct, there are no duplicate tuples.

The order of attributes has no significance.

The order of tuples has no significance,

9

Properties of Relations (2)

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S10 Misc Topics

Superkey – An attribute, or set of attributes, that uniquely identifies a tuple within a relation.

Candidate key – A Superkey, such that no proper subset is superkey within the relation.

A candidate key, k, for a relation R has two properties:

1) Uniqueness: In each tuple of R, the value of k uniquely identify the tuple.

2) Irreducibility – no proper subset of k has the uniqueness property 10

Relational Keys (1)

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S11 Misc Topics

They may be several candidate keys for a relation.

Composite key – A key consists of more than one attribute.

Exampes:

1) Do you think “city” in Branch relation is a candidate key? The answer is no. Why? Because London has two branch offices, therefore, the attribute “city” cannot be a candidate key.

2) Is “branchNo” a candidate key? Yes, Why? By Examining “branchNo”, each branch office has a unique branchNo,

3) Is postcode is a candidate key? Yes.. Why? 11

Relational Keys (2)

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S12 Misc Topics

Primary key: The candidate key that is selected to identify tuples uniquely within the relation

Alternate keys – The Candidate keys that are not selected to be the primary key.

Exampes:

1) In the Branch Relation, we can choose branchNo as the primary key and

2) Postcode as an alternate key.

12

Relational Keys (3)

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S13 Misc Topics

13

Relational Keys (4)

– Foreign key: An attribute, or a set of attributes, with one relation that matches the candidate key of some (possibly the same) relation.

– branchNo appeared in two relations: Branch and Saff relations

– branchNo is a primary key in Branch relation and it is a foreign key in the Staff relation.

© M.E. Fayad 2002-2005 SJSU – CmpE --- M.E. Fayad L8-2-S14 Misc Topics

T/F

1. Each cell of the relation contains exactly on atomic (single) value.

2. Primary key is the candidate key that is selected to identify tuples uniquely within the database.

3. Foreign key is an attribute or a set of attributes within on relation that matches the candidate key of some relation.

4. The degree of a relation is the number of tuples it contains.

14

Discussion Questions