Mid term Exam

COVERS chapters 1-3, 7-8

Two partsIn class

Take home part (given on Oct 29th, Due Nov5th in class)

System catalogs

Information about database• It is automatically created everytime a

database is created• It contains tables like:• Systables• Syscolumns• Sysindexes• Sysviews

In ORACLE

User_catalog• SQL> desc user_catalog;• Name Null? Type• ----------------------------------------- --------

----------------------------• TABLE_NAME NOT NULL

VARCHAR2(30)• TABLE_TYPE

VARCHAR2(11)

• Select * from user_catalog;

USER_TABLES

• User_objects

• User_tab_columns

• User_views

You can query using select statements

To get constraints

• SQL> select owner, constraint_type• from user_constraints• where table_name ='WROTE'; 2 3

• OWNER C• ------------------------------ -• AGGARWAL P• AGGARWAL R• AGGARWAL R

• Note P for primary• R for referential

Systables in ORACLEhttp://www.tek-tips.com/viewthread.cfm?qid=1292962&page=3

• there is no such object as systables in oracle. What you are looking for is

dba_tables - All tables in system, only visible to administrators

all_tables - All tables in all schema's that the connected user has access to.

user_tables - all tables in the connected users schema. Bill

Oracle DBA/Developer

Ch 4 Entity Relationship (ER Modeling)

Business rules

Business rules are precise statements, derived from a detailed description of the organization's operations. When written properly, business rules define one or more of the following modeling components:– entities– relationships– attributes– connectivities– cardinalities– constraints

Because the business rules form the basis of the data modeling process, their

precise statement is crucial to the success of the database design.

because the business rules are derived from a precise description of operations,

design's success depends on the accuracy of the description of operations.

Examples of business rules are:

• An invoice contains one or more invoice lines.• Each invoice line is associated with a single invoice.• A store employs many employees.• Each employee is employed by only one store.• A college has many departments.• Each department belongs to a single college. (This

business rule reflects a university that has multiple colleges such as Business, Liberal Arts, Education, Engineering, etc.)

• A driver may be assigned to drive many different vehicles.

• A client may sign many contracts.• Each contract is signed by only one client.

DATA MODEL

• Representation of complex real-world .• Goal is to create a DB that is accurate representation of

data needs • and real world data relationships• A good DB design begins with a good data model• ..a method for determining "WHAT" data and

relationships should be • stored in DB and not "HOW" data will be stored or

processed• Hardware/software indep.

– ..development is an iterative process

THE E-R Model:

• Translates different data view into a common framework

• Defines data processing and constraints requirements

• Peter Chen (1976) was the first person to introduce the concept of ER modeling.

• An ER model is a detailed logical representation for an organization

• ER Building Blocks (p 124)

ENTITIES & ATTRIBUTES

Entities:– An object of interest– Person– Place– Event– concept– An entity type consists of entity instances

Attributes– Properties of an entity– Describes an entity– Attributes have DOMAINS.– Domain is a set of possible values. Two attributes can share the – same domain

Derived Attributes:

• These are calculated or extracted from other attributes

• Ex: total sales

• Typically a derived field is not stored in the DB, calculated as needed

Relationship:Association between entities

• 1:1• 1:m• m:n• Unary...within itself• Binary..with two entities• Ternary..with three entities

Unary (recursive):Entity has a relationship to itself

• 1:1• 1:m• m:n

Super & sub type entities (used extensively in Object oriented systems)

• One challenge is to RECOGNIZE and represent entities that are

• almost the same, i.e., the share some properties but also have

• distinct properties

• Ex: COMPUTER• Mainframe• Minicomputer• personal• EMPLOYEE• Full time• Part time

Relationship:• IS-A super, sub entity relationships are of the type “IS A”;

– Ex: full time employee “IS AN” employee• HAS-A: between two entities..STUDENT “HAS A” relationship with

CLASS

Inheritance

• All attributes of a super type become attributes of the subtype

• Each attribute should be located at the highest level in the hierarchy

CARDINALITY (useful in getting approximate database size)

(MIN and Max) Number of instances of one entity that can be associated with each

instance of the other entity• Place the appropriate number beside the entity• Minimum• Maximum

Student <_------_>class(1,6) (1,40)

• student _-------_> major• patient_------_> pat_history

Database name: Ch03_BeneCoTable name: EMPLOYEE Table name: BENEFIT

Table name: JOB Table name: PLAN

Draw the ERD

Example

if you were to develop an ER model for a video rental store, you would note that tapes can be rented more than once and that customers can rent more than one tape.

Q1/136

Entities

• COMPANY

• DEPARTMENT

• DEPENDENT

• EMPLOYMENT HISTORY

Q3/p137

Q7/p139

Q2/ p 136 & Q8/p139

Q2/p136

• A COURSE does not necessarily generate a class during each training period. (Some courses may be taught every other period or during some other specified time frames.

• Each CLASS must be related to a COURSE.

• Some instructors may teach a class or do research

• Not all trainees are likely to be enrolled in classes during some time period.

• A trainee can take more than one class, and each class contains many (10 or more) trainees, so there is a M:N relationship between TRAINEE and CLASS. (Therefore, a composite entity is used to serve as the bridge between TRAINEE and CLASS.)

• A class is taught by only one instructor, but an instructor can teach up to two classes. Therefore, there is a 1:M relationship between INSTRUCTOR and CLASS.

• Finally, a COURSE may generate more than one CLASS, while each CLASS is based on one COURSE, so there is a 1:M relationship between COURSE and CLASS.

ERD Q2/p170

Building an ER modelQ8/P139

Identify entities

DINNER

ENTRÉE

GUEST

Relationships

• Each dinner is based on a single entrée, but each entrée can be served at many dinners

ENTREE DINNER

Cardinality

Cardinality

One entrée can be part of a min of 1 dinner and a max of many dinners, say n

One dinner can be part of a minimum of one entrée and a max of one entrée

(1,N) (1,1)

entree dinner

Relationship between DINNER and GUEST

Note there are TWO relationships

A guest can attend many dinners

Vice versa

A guest can have many dinner invitations

Vice versa

invitationDinner Guest

Relationship between DINNER and GUEST

Note there are TWO relationships

A guest can attend many dinners

Vice versa

Dinner GuestAttend

Relationship between DINNER and GUEST

Second relationship

A guest can have many dinner invitations

Vice versa

Dinner Guestinvitation

Converting m:n into two 1:m

since Guest and DINNER is m:n we can break into TWO 1:m

i.e ATTEND entity is intersection of DINNER & GUEST

DINNER ATTEND GUEST

cardinality

What is ATTEND entity ? a combination of a dinner and a guest

• What’s the min number of DINNER in ATTEND? 1

• (a dinner must be part of at lest ONE function (ATTEND)

Max number? N (assuming N is total # of dinners)

An attend can be part as a min part of one dinner and a max of ONE dinner also

• what’s the min number of ATTEND a GUEST can have?0

• (a guest may not attend any dinner) or they may attend a max of N dinners

DINNER ATTEND GUEST

(1,N) (1,1) (1,1) (0,N)

• Same concepts can be applied to INVITATION intersection entity

ERD Q 8/p139

EX: Convert following ERD into relations

assume a student can be advised by one professor but a professor can advise many students, a club can have many students but a student can join only one club, then the ERD will look as

STUDENT

PROFESSOR CLUB

Relations will be

STUDENT (St_ID, st_name,…,Club_ID, Prof_ID)

Note: we must account for both relationships in STUDENT entity (student, professor) AND (student, club)

CLUB(Club_ID, location,date_established,..)

PROFESSOR(Prof_ID, Prof_name, specialty,..)