lecture 02 - db development

7/30/2019 Lecture 02 - DB Development

1/45

2


2/45

()?

...

*!

*

ISO/IEC 12207:1995Information Technology Software Life Cycle Processes ,

. ,, , .

2
http://ru.wikipedia.org/wiki/%D0%9F%D1%80%D0%BE%D1%86%D0%B5%D1%81%D1%81http://ru.wikipedia.org/wiki/%D0%94%D0%B5%D1%8F%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D0%BE%D1%81%D1%82%D1%8Chttp://ru.wikipedia.org/wiki/%D0%97%D0%B0%D0%B4%D0%B0%D1%87%D0%B0http://ru.wikipedia.org/wiki/%D0%97%D0%B0%D0%B4%D0%B0%D1%87%D0%B0http://ru.wikipedia.org/wiki/%D0%94%D0%B5%D1%8F%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D0%BE%D1%81%D1%82%D1%8Chttp://ru.wikipedia.org/wiki/%D0%9F%D1%80%D0%BE%D1%86%D0%B5%D1%81%D1%81


3/45


4/45

4

-...


5/45

5

-...


6/45

6

...


7/45

7

Puzzle

... ...


8/45

8

?

:

.

.

.

.

.


9/45

9

-

:

;

.


10/45


11/45

Levels of Abstraction

Views describe howusers see the data.

Conceptual schemadefines logicalstructure

Physical schemadescribes the filesand indexes used.

(sometimes called the

ANSI/SPARC model)

Physical Schema

Conceptual Schema

View 1 View 2 View 3

DB

Users


12/45

Example: University Database

Conceptual schema:

Students(sid: string, name: string,login: string, age: integer, gpa:real)

Courses(cid: string, cname:string,

credits:integer) Enrolled(sid:string, cid:string,

grade:string)

External Schema (View):

Course_info(cid:string,

enrollment:integer)

Physical schema:

Relations stored as unordered files.

Index on first column of Students.

Physical Schema

Conceptual Schema


DB


13/45

Data Independence

Applications insulated fromhow data is structured andstored.

Logical data independence:Protection from changes in

logicalstructure of data.

Physical dataindependence: Protectionfrom changes inphysical

structure of data.

Q: Why are theseparticularly important forDBMS?

Physical Schema

Conceptual Schema


DB


14/45

Entity-Relationship Model

" - " " - ", ER -

.

(entity-relationship diagram), - .

(entity set).

- , -


15/45

15


16/45

16

Database design lifecycle

Requirements analysis

User needs; what must database do?

Conceptual design

High-level description; often using E/R model

Logical design

Translate E/R model into (typically) relational schema

Schema refinement

Check schema for redundancies and anomalies

Physical design/tuning

Consider typical workloads, and further optimise

Today


17/45

17

Todays lecture

E/R modelling

Entities

Attributes

Relationships Constraints on relationships

Extended E/R modelling

Object ideas


18/45


19/45

19

E/R basics

An entity is a real-world object that isdistinguishable from other objects

Each entity has attributes (with domains)

A particular entity will have a value for each of itsattributes

An entity type defines a set of entities that havethe same attributes

An entity set is the collection of all entities of aparticular entity type (at a particular point intime)


20/45

20

Entities and attributes

Entity types are drawn as rectangles, e.g.

Attributes are drawn as ovals, andattached to the entity sets with lines, e.g.

Employees

NI dob

Name

Employees


21/45

ER Diagrams - Symbols


22/45

Summary of Symbols


23/45

23

Key attributes

A key attribute of an entity type is anattribute whose values are distinct foreach entity

Sometimes several attributes (a compositeattribute) together form a key

NB: Such a composite should be minimal

We underline key attributes

NI dobName

Employees


24/45

24

Relationships

A relationship type among two or moreentity types defines a set of associationsbetween entities from those types

Mathematically, relationship type RR E1 En.

The set of instances of the relationshiptype is called the relationship set


25/45

25

Relationships in E/R

Relationship types are represented bydiamonds

They connect the participating entity types

with straight lines, e.g.

Works_in

NI dobName

Employees

DID budgetdname

Departments


26/45

26

Relationship set diagrams

Sometimes its useful to represent therelationship set diagrammatically

e1

e2e3

e4

e5

d1

d2

d3

d4

d5

r1

r2

r3

r4


27/45

27

Relationship attributes

Relationships can also have attributes

NB: A relationship must be uniquelydetermined by the entities, without referenceto the relationship attributes

Works_in

NI dobName

Employees

DID budgetdname

Departments

since


28/45

28

N-ary relationships

Although relatively rare, we can have n-ary relationships, e.g.

Works_in2

NI dob

Name

Employees

DID budget

dname

Department

since

Locationsaddress capacity


29/45

29

Recursive relationships

Each entity type in a relationship plays aparticular role, which is associated with a rolename (this is usually suppressed)

An recursive relationship is when an entity

type plays more than one role in the relationshiptype

In this case the role name is required


30/45

30

Recursive relationships in E/R

e.g.

Employees

Reports-to

NI

namedob

subordinatesupervisor


31/45

31

Constraints on relationship types

For example: An employee can work in many departments;

a department can have many employees

In contrast, each department has at most one

manager

Thus we need to be able to specify thenumber of relationship instances that anentity can participate in.

For binary relationships the possible ratiosare: 1:1, 1:N, N:1, M:N


32/45

32

Cardinality ratios1:1 1:N

M:N


33/45

33

Cardinality ratios in E/R

M:N

N:1

1:1

M N

N 1

1 1

Note: Sometimes this is written using different arrowheads


34/45

Types of Binary Relationships

Representation of Many-One

Many-many

Many-one E/R: arrow pointing to one.

One-oneMany-one


35/45

35

Participation constraints

Every department must have a manager

This is an example of a participation

constraint The participation of an entity set, E, in a

relationship set R is said to be totalif

every entity in E participates in at leastone relationship in R. (If not itsparticipation is said to be partial)


36/45

36

Participation in E/R diagrams

Total participation is displayed as a boldline between the entity type and therelationship

NB. Sometimes this is written as a double line

Manages

NI dobName

Employees

DID budgetdname

Department

since

1 N


37/45

37

Weak entity types

An entity type may not have sufficientattributes to form a primary key

Such an entity type is called a weak

entity type A weak entity can only be identified

uniquely by considering the primary key ofanother (owner) entity


38/45

38

Weak entity types cont.

Thus the owner and weak entity typesmust participate in a 1:N relationship

Weak entity set must have total

participation in this identifyingrelationship set.

Employees

NIName

Policy Dependents

CostpName age

1 N


39/45

39

Extended E/R modelling

What weve seen so far is classic E/R

Over the years a number of features havebeen added to the model and the

modelling process These features include:

Sub- and super-

classes Specialisation

Generalisation

Categories

Higher/Lower-level

entity sets Attributeinheritance

Aggregation


40/45

40

ISA hierarchies

We can devise hierarchies for our entitytypes

If we declare

A ISA B, everyA entity isconsidered tobe a B entity

Employees

ISA

Temp_Emp Contract_Emp

hoursrate cid

NI Name dob


41/45

41

Attribute inheritance

As wed expect, attributes of superclassesare inherited by the subclasses.

Thus: Temp_Emp also has attributes NI,

Name and dob

In fact, subclasses inherit relationships too


42/45

42

Aggregation

Suppose we have an entity set ofProjectsand that each project is sponsored by oneor more departments; thus

Sponsors DepartmentsProjects

PID

start

budget

since

budgetDID

dname

NM


43/45

43

Aggregation cont.

Suppose that employees are assigned tomonitor a sponsorship

Monitors should be a relationship between

Employees and the Sponsorsrelationship Aggregation allows us to indicate that a

relationship set participates in anotherrelationship set

Use dashed box


44/45

44

Aggregation cont.

Sponsors DepartmentsProjects

PID

startbudget

since

budgetDID

dname

Employees

nameNI

Monitors until

N M

A Data Model from the


45/45

45

A Data Model from theEuropean Bioinformatics Institute (EBI)

See http://intact.sourceforge.net/uml/intactCore.gif

lecture 02 - db development

Documents