DBMS Architecture

How should DBS be organized?

Chapter Two

1

Agenda (Chapter two) Reality, Data & Metadata

The Three Levels of DBS Architecture

External View, Conceptual View, Internal View

Schemas, Mappings, and Instances

The Database Management System (DBMS)

Functions of DBMS

Requirements of DBMS with Respect to Database

Languages (DDL and DML)

Roles in Database Environment

2

Reality, metadata and data value Reality is what exists in the real world.

This reality might be in a physical or logical form.

When developing a database or information system,

representation of the reality in the computer system is the first

step.

The representation would be by considering the properties the

reality exhibits.

When these properties assume a specific value it would represent

the real world object for which data is required to be captured for.

Thus any data model will be having a representation mechanism

for the building blocks of data representation.

3

Cont…

Real world can be represented using its building blocks.

The building blocks vary based on the kind of reality we want

to represent.

When it comes to data representation, the building blocks

are:

Entities

Attributes

Relationship

4

ENTITIES Real world physical or logical object for which data need

to be captured for

Persons, places, things etc. which the organization has to deal with.

The name given to an entity should always be a singular noun descriptive of each item to be stored in it.

E.g.: student NOT students

5

Cont… Existence Dependency: the dependence of an entity on the

existence of one or more entities.

Weak entity : an entity that can not exist without the entity with which it has a relationship – it is indicated by a double rectangle or dotted line (various modeling approaches)

Entity will be realized as relations or tables later

Relations can also describe relationships (will be discussed later)

Every relation has a schema, which describes the columns, or fields the relation itself corresponds to our familiar notion of a table

A relation is a collection of tuples, each of which contains values for a fixed number of attributes

6

ATTRIBUTES Properties used to describe each Entity or real world object.

These attributes will assume a value to represent a single

occurrence of that real world object class

The items of information which characterize and describe

these entities.

Attributes are pieces of information ABOUT entities.

The analysis must of course identify those which are actually

relevant to the proposed application.

Attributes will give rise to recorded items of data in the

database

7

Cont…

At this level we need to know such things as:

Attribute name (be explanatory words or phrases)

The domain from which attribute values are taken (A

DOMAIN is a set of values from which attribute values may be

taken.)

Each attribute has values taken from a domain.

For example, the domain of Name is string and that for salary

is real

8

Cont…

Whether the attribute is part of the entity identifier

(attributes which just describe an entity and those which help

to identify it uniquely)

Whether it is permanent or time-varying (which

attributes may change their values over time)

Whether it is required or optional for the entity (whose

values will sometimes be unknown or irrelevant)

9

Types of Attributes

Simple (atomic) Vs Composite attributes

Simple : contains a single value (not divided into

sub parts)

E.g. Age, gender

Composite: Divided into sub parts (composed of

other attributes)

E.g. Name, address

10

Cont…

Single-valued Vs multi-valued attributes

Single-valued : have only single value (the value may change but has only one value at one time) E.g. Name, Sex, Id. No. color_of_eyes

Multi-Valued: have more than one value E.g. hobby Address, dependent-name

Person may have several college degrees

11

Cont…

Stored vs. Derived Attribute Stored : not possible to derive or compute

E.g. Name, Address

Derived: The value may be derived (computed) from the values

of other attributes.

E.g. Age (current year – year of birth)

Length of employment (current date- start date)

Profit (earning-cost)

G.P.A (grade point/credit hours)

12

Cont…

Null Values (Null “Ok” attributes) NULL applies to attributes which are not applicable or

which do not have values.

You may enter the value NA (meaning not applicable)

Value of a key attribute can not be null.

Default value - assumed value if no explicit value

13

Entity Vs Attributes When designing the conceptual specification of the database, one

should pay attention to the distinction between an Entity and an

Attribute.

Consider designing a database of employees for an organization:

Should address be an attribute of Employees or an entity

(connected to Employees by a relationship)?

If we have several addresses per employee, address must be an

entity (attributes cannot be set-valued/multi valued)

If the structure (city, Woreda, Kebele, etc) is important, e.g. want

to retrieve employees in a given city, address must be modeled as

an entity (attribute values are atomic)

14

RELATIONSHIPS Associations between entities which exist and must be taken into

account when processing information.

In any business processing one object may be associated with

another object due to some event.

Such kind of association is what we call a RELATIONSHIP between

entity objects

A relationship should be named by a word or phrase which explains its function

For each RELATIONSHIP, one can talk about the Number of Entities and the Number of Tuples participating in the association.

These two concepts are called DEGREE and CARDINALITY of a relationship respectively

15

Cont…

Degree of a Relationship

An important point about a relationship is how many entities

participate in it.

The number of entities participating in a relationship is called

the DEGREE of the relationship.

16

Cont… Among the Degrees of relationship, the following are the

basic: UNARY/RECURSIVE RELATIONSHIP: Tuples/records of a Single

entity are related withy each other.

BINARY RELATIONSHIPS: Tuples/records of two entities are associated in a relationship

TERNARY RELATIONSHIP: Tuples/records of three different entities are associated

And a generalized one:

N-NARY RELATIONSHIP: Tuples from arbitrary number of entity sets are participating in a relationship.

17

Cont… Cardinality of a Relationship

Another important concept about relationship is the number of instances/tuples that can be associated with a single instance from one entity in a single relationship.

The number of instances participating or associated with a single instance from an entity in a relationship is called the CARDINALITY of the relationship.

18

Cont…

The major cardinalities of a relationship are: ONE-TO-ONE: one tuple is associated with only one other

tuple.

E.g. Building – Location as a single building will be located in a single location and as a single location will only accommodate a single Building.

ONE-TO-MANY, one tuple can be associated with many other tuples, but not the reverse.

E.g. Department-Student as one department can have multiple students.

19

Cont… MANY-TO-ONE, many tuples are associated with one tuple

but not the reverse.

E.g. Employee – Department: as many employees belong to a single department.

MANY-TO-MANY: one tuple is associated with many other tuples and from the other side, with a different role name one tuple will be associated with many tuples

E.g. Student – Courseas a student can take many courses and a single course can be attended by many students.

What do govern the cardinality and degree of a given relationship?

20

Three levels/views of DBS

21

Database Architecture DBMSs do not all confirm to the same architecture.

The three-level architecture forms the basis of modern

database architectures.

Agreement with the ANSI/SPARC (American National

Standards Institute- Standards Planning and Requirement

Committee) study group on Database Management

Systems.

22

Cont…

The architecture for DBMSs is divided into

three general levels: 1.External-user

2.Conceptual-logical

3.Internal-physical

23

3 Level ANSI/SPARC Architecture

• Proposed to support DBMS characteristics of:

• Program-data independence. • Data definition is separated from the application

• Data Sharing • Support of multiple views of the data

24

Cont…

Three levels of abstractions in describing data For better understanding of DB functionalities Made databases more independent of

application Became a standard for the organisation of

DBMS

25

The Three Levels of DBS Architecture:

ANSI-SPARC DB Architecture

26

Cont…

External Level: Users' view of the database.

concerned with the way individual users see the data

Describes that part of database that is relevant to a particular

user.

Different users have their own customized view of the database

independent of other users.

27

Cont…

Conceptual Level: Community view of the database.

Describes what data is stored in database and relationships

among the data

can be regarded as a community user view ­ a formal

description of data of interest to the organisation, independent

of any storage considerations.

28

Cont…

Internal Level: Physical representation of the database on the computer.

Concerned with the way in which the data is actually stored

Storage spacing allocation for data

Record description for storage

Describes how the data is stored in the database.

29

External (Sub) Schema o defines the external view of data as seen by a user or

program

Conceptual Schema o defines the logical view of data as seen by all users and

programs

Physical (Internal) Schema o defines the physical view of data as seen by a DBMS

Schema for the level

30

Purpose 3-Level DB architecture All users should be able to access same data.

Since the database is having a shared data feature where all the data is stored in one location and all users will have their own customized way of interacting with the data.

A user's view is unaffected or immune to changes made in other views.

Since the requirement of one user is independent of the other, a change made in one user’s view should not affect other users.

31

Cont… Users should not need to know physical database storage

details.

As there are naïve users of the system, hardware level or physical details should be a black-box for such

users.

DBA should be able to change database storage structures without affecting the users' views.

A change in file organization, access method should not affect the structure of the data which in turn will have no effect on the users.

32

Cont…

Internal structure of database should be unaffected by changes to physical aspects of storage.

DBA should be able to change conceptual structure of database without affecting all users.

In any database system, the DBA will have the privilege to change the structure of the database,

like adding tables,

adding and deleting an attribute,

changing the specification of the objects in the database.

33

ANSI-SPARC Architecture and Database Design Phases

34

Example

35

• Different people

have different

views of the

database…these

are the external

schema

• The internal

schema is the

underlying

design and

implementation

Three-schema architecture

36

Developing the three-tiered architecture

37

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

View 1 View 2 View 3

DB

38

Conceptual Layer

Physical Layer

Base Tables

Stored Tables ...

External Layer View View View

39

Physical View

database

• The DBMS must know

– exact physical location

– precise physical structure

Name (20 characters) Address (40 characters)

NID (10 char) Designation (15 char)

A.B.C. De Silva |222, Galle Road, Colombo |

650370690V|Senior Lecturer

Employee record

40

database

Logical View

• The user/application must

know

– existence

– logical reference Employee

Address 222, Galle Road, Colombo

Name A.B.C. De Silva

Designation Senior Lecturer

NID 650370690V

41

Conceptual Layer

• The conceptual model is a logical representation of

the entire contents of the database.

• The conceptual model is made up of base tables.

• Base tables are “real” in that they contain physical

records.

Table

Table

42

database

External View

• The user/application see

– authorised data

– own format

Lecturer

Department Dept. of Computer Science

Name A.B.C. De Silva

Designation Senior Lecturer Age 35

43

• External Views Allows to

– hide unauthorised data

e.g. salary, date of birth

– provide user view

e.g. view employee name, designation,

department data taken from employee and

department files

– derive new attributes

e.g. age derived from date of birth

External View cont.

44

• External Views Allows to

– change unit of measurement

e.g. show age in years or months

– define security levels

e.g. update access to employee file

read-only to department file

External View cont.

45

External Layer

• The external model represents how data is

presented to users.

• It is made up of view tables. View tables

are "virtual"-- they do not exist in physical

storage, but appear to a user as if they did

View

View

46

Data Independence This is a prime advantage of a database

In conventional systems applications are data-dependent

For example, if a file is stored in indexed sequential form then an application must know that the index exists

the file sequence (as defined by the index),

The internal structure of the application will be built around

this knowledge.

If, for example, the file was to be replaced by another file

with different indexing structure major modifications would

have to be made to the application.

47

Cont... Such an application is data-dependent

it is undesirable to allow applications to be data-dependent

the DBA must have the freedom to change storage structure or access strategy in response to changing requirements without having to modify existing applications.

Data independence can be defined as

‘The immunity of applications to change in storage structure and access strategy’.

Data independence is the ability to change the schema at one level of the database system without changing the schema at the next higher level. There are two types

Logical data independence

Physical data independence

48

Data Independence Applications insulated from how

data is structured and stored.

Logical data independence:

Protection from changes in logical

structure of data.

Physical data independence:

Protection from changes in physical

structure of data.

Question:

Why are these particularly

important for DBMS?

Physical Schema

Conceptual Schema

View 1 View 2 View 3

DB

49

Cont…

Logical Data Independence:

Refers to immunity of external schemas to changes in conceptual

schema.

Conceptual schema changes e.g. addition/removal of entities should

not require changes to external schema or rewrites of application

programs.

The capacity to change the conceptual schema without having to

change the external schemas and their application programs

50

Cont… Physical Data Independence The ability to modify the physical schema without changing the

logical schema Applications depend on the logical schema In general, the interfaces between the various levels and

components should be well defined so that changes in some parts do not seriously influence others.

The capacity to change the internal schema without having to change the conceptual schema

Refers to immunity of conceptual schema to changes in the internal schema

Internal schema changes e.g. using different file organizations, storage structures/devices should not require change to conceptual or external schemas.

51

Schemas, Mappings, and Instances

52

Schema Vs data Information in the database is subdivided into two concepts:

Schema

Data

Schema

Schema is the concept of how information relates to other pieces of information, and how information should be grouped.

Schema describes how data is to be structured - defined at set-up time, rarely changes (part of the "metadata")

Comparable to types and variables in programming languages

External- different views of data

Conceptual- description entities, attributes and r/n ships

Internal schema- description of representing fields

53

Cont… Data

Data is actual "instance" of database, may change rapidly

Data is the concept of the actual information users want to store

in the database.

You can only store data in structures which the schema

provides, so we must ensure that the schema is correct.

54

Schemas versus Instances

• Database Schema: • The description of a database. • Includes descriptions of the database structure and the constraints that

should hold on the database.

• Schema Diagram: A diagrammatic display of (some aspects of) a database schema.

• Schema Construct: A component of the schema or an object within the schema, e.g., STUDENT, COURSE.

• Database Instance:

• The actual data stored in a database at a particular moment in time.

• Also called database state (or occurrence).

55

Database Schema Vs. Database State • Database State:

• Refers to the content of a database at a moment in time.

• Initial Database State:

• Refers to the database when it is loaded

• Valid State:

• A state that satisfies the structure and constraints of the database.

• The database schema changes very rarely.

• The database state changes every time the database is updated (inserting

new data, changing an existing data or deleting an existing data).

• Schema is also called intension, whereas state is called extension.

56

Mappings • Mapping is a process of converting one level to another level. • Mappings among schema levels are needed to transform

requests and data. • Programs refer to an external schema, and are mapped by the

DBMS to the internal schema for execution • There are two levels of mapping

The conceptual/internal mapping:

defines conceptual and internal view correspondence

specifies mapping from conceptual records to their stored counterparts

An external/conceptual mapping:

defines a particular external and conceptual view correspondence

57

Cont…

A change to the storage structure definition means that the

conceptual/internal mapping must be changed accordingly,

so that the conceptual schema may remain invariant,

achieving physical data independence.

A change to the conceptual definition means that the

conceptual/external mapping must be changed accordingly,

so that the external schema may remain invariant, achieving

logical data independence.

58

The Database Management System

(DBMS)-Functions and Languages

59

The DBMS-Functions and Languages

Database Management System (DBMS) is a Software package

used for providing

a systematic method for creating, updating, storing,

retrieving data in a database.

the service of controlling data access, enforcing data

integrity, managing concurrency control, and recovery.

EFFICIENT, CONVENIENT and SAFE MULTI-USER (many

people/programs accessing same database, or even same data,

simultaneously)storage of and access to MASSIVE amounts of

PERSISTENT (data outlives programs that operate on it) data.

60

Cont…

A full scale DBMS should at least have the following services

to provide to the user

Data storage, retrieval and update in the database

A user accessible catalogue (metadata)

Transaction support service: ALL or NONE transaction, which

minimize data inconsistency.

Concurrency Control Services: access and update on the database by

different users simultaneously should be implemented correctly.

Recovery Services: a mechanism for recovering the database after a failure

must be available.

61

Cont…

Authorization Services (Security): must support the implementation of access and authorization service to database administrator and users.

Support for Data Communication: should provide the facility to integrate with data transfer software or data communication managers.

Integrity Services: rules about data and the change that took place on the data, correctness and consistency of stored data, and quality of data based on business constraints.

62

Cont… Services to promote data independency between the data

and the application

Utility services: sets of utility service facilities like Importing data

Statistical analysis support

Index reorganization

Garbage collection

63

Cont…

Typical DBMS Functionality (simply)

Define a particular database;

Construct or Load the initial database

Manipulate the database;

Process and Share for a set of concurrent users and application

programs

64

Database languages

65

Database languages A DBMS is software package used to develop, manage, and

maintain databases.

Each DBMS should have facilities to define the database, manipulate the content of the database and control the database.

These facilities will help the designer, the user as well as the database administrator to discharge their responsibility in

designing,

using and

managing the database.

66

Cont…

The two major categories of languages are

Data Definition Language (DDL)

Data Manipulation Language (DML)

But there is also a third category

Data Control Language (DCL)

67

Cont…

Data Definition Language (DDL):

Language used to define each data element required by the

organization.

Commands for setting up schema or the intension of database

These commands are used to setup a database, create,

drop and alter table with the facility of handling constraints

68

Cont… Allows DBA or user to describe and name entities, attributes and

relationships required for the application.

Specification notation for defining the database schema

Example:

create table Student ( StudentID char(10),

FirstNAme char(15), LastName char(15), Age integer )

69

Cont…

Some more command examples: CREATE - to create objects in the database

ALTER - alters the structure of the database

DROP - delete objects from the database

TRUNCATE - remove all records from a table, including all

spaces allocated for the records are removed

COMMENT - add comments to the data dictionary

RENAME - rename an object

70

Cont…

Data Manipulation Language (DML):

Is a core command used by end-users and programmers to

store, retrieve, and access the data in the database e.g. SQL

Since the required data or Query by the user will be extracted

using this type of language, it is also called "Query Language“

Provides basic data manipulation operations on data held in the

database.

Language for accessing and manipulating the data organized by

the appropriate data model

71

Cont…

DML can be in two forms Procedural DML:

user specifies what data is required and how to get the data.

Non-Procedural DML:

user specifies what data is required but not how it is to be retrieved

SQL is the most widely used non-procedural language query language

72

Cont… E.g. find the name of the passenger with passport number

EP0453623

select Passenger.Name from passenger where passenger.passposrtNo = ‘EP0453623’

73

Cont…

Some more command examples:

SELECT - retrieve data from the a database

INSERT - insert data into a table

UPDATE - updates existing data within a table

DELETE - deletes all records from a table, the space for the records

remain

CALL - call a PL/SQL or Java subprogram

LOCK TABLE - control concurrency

74

Cont…

Still one can consider additional DB languages

called: Data Control Language (DCL)

Database is a shared resource that demands control of data

access and usage.

The database administrator should have the facility to control

the overall operation of the system.

75

Cont… Data Control Languages are commands that will help the

Database Administrator to control the database.

The commands include commands like granting privileges

to access the database or particular object within the database

and to store or remove database transactions

Some examples of Data Control Language (DCL)

statements.

GRANT - gives user's access privileges to database

REVOKE - withdraw access privileges given with the GRANT

command

76

Components of a DB Environment The DBMS is software package that helps to design, manage,

and use data using the database approach.

Taking a DBMS as a system, one can describe it with respect to it environment or other systems interacting with the DBMS.

The DBMS environment has five components.

To design and use a database, there will be the interaction or integration of Hardware, Software, Data, Procedure and People.

77

Cont…

Hardware:

are components that one can touch and feel.

These components are comprised of various types of personal computers,

mainframe or any server computers to be used in multi-user system,

network infrastructure, and

other peripherals required in the system.

78

Cont…

Software:

Collection of commands and programs used to

manipulate the hardware to perform a function.

These include components like the DBMS software,

application programs, operating systems, network

software, language software and other relevant

software

79

Cont…

Data: Since the goal of any database system is to have better control of

the data and making data useful, Data is the most important component to the user of the database.

There are two categories of data in any database system: that is Operational and Metadata.

Operational data is the data actually stored in the system to be used by the user.

Metadata is the data that is used to store information about the database itself.

The structure of the data in the database is called the schema, which is composed of the Entities, Properties of entities, and relationship between entities.

80

Cont…

Procedure:

The rules and regulations on how to design and use a database.

It includes procedures like

how to log on to the DBMS,

how to use facilities,

how to start and stop transaction,

how to make backup,

how to treat hardware and software failure,

how to change the structure of the database.

81

Cont…

People:

those people in the organization that are responsible or play a role in designing, implementing, managing, administering and using the resources in the database.

This component includes group of people with high level of knowledge about the database and the design technology to other with no knowledge of the system except using the data in the database.

82

Development cycle and

Roles in Database Envr’t

83

Roles and Development cycle in DB Environment

Roles in database environment will be at different levels of

database design and development

As it is one component in most information system

development tasks, there are several steps in designing a

database system.

Here more emphasis is given to the design phases of the

system development life cycle.

84

Steps in DB Design…

Accordingly the major steps in database design are;

1. Planning: that is identifying information gap in an

organization and propose a database solution to

solve the problem.

2. Analysis: that concentrates more on fact finding

about the problem or the opportunity. Feasibility

analysis, requirement determination and

structuring, and selection of best design method

are also performed at this phase

85

Cont…

3. Design: in database designing more emphasis is given to this

phase.

The phase is further divided into three sub-phases.

Conceptual

Logical

Physical

86

Conceptual Design

Logical Design

Physical Design

Cont…

Conceptual Design concise description of the data, data type, relationship between

data and constraints on the data. There is no implementation or physical detail consideration. Used to elicit and structure all information requirements Conceptual design is the process of constructing a model of the

information used in an enterprise, independent of any physical considerations.

It is the source of information for the logical design phase. Mostly uses an Entity Relationship Model to describe the data at

this level. After the completion of Conceptual Design one has to go for

refinement of the schema, which is verification of Entities, Attributes, and Relationships

87

Cont… Logical Design: a higher level conceptual abstraction with selected specific data model to

implement the data structure. It is particular DBMS independent and with no other physical

considerations. Logical design is the process of constructing a model of the information

used in an enterprise based on a specific data model (e.g. relational, hierarchical or network or object), but independent of a particular DBMS and other physical considerations.

It includes Normalization process Collection of Rules to be maintained Discover new entities in the process Revise attributes based on the rules and the discovered Entities

88

Cont… Physical Design: physical implementation of the upper level design of the

database with respect to internal storage and file structure of the database for the selected DBMS.

To develop all technology and organizational specification. Physical design is the process of producing a description of

the implementation of the database on secondary storage. -- defines specific storage or access methods used by database

It Describes the storage structures and access methods used to achieve efficient access to the data.

Tailored to a specific DBMS system -- Characteristics are function of DBMS and operating systems

Includes estimate of storage space

89

Cont…

4. Implementation: the testing and deployment of the

designed database for use.

5. Operation and Support: administering and

maintaining the operation of the database system and

providing support to users.

90

People in DB environment

As people are one of the components in DBMS environment, there are group of roles played by different stakeholders at the different levels of the designing and operation of a database system

DB Administrator DB designer Application programmer and system analyst User

91

Cont…

Database Administrator (DBA)

Responsible to oversee, control and manage the database

resources (the database itself, the DBMS and other related

software)

Authorizing access to the database

Coordinating and monitoring the use of the database

Responsible for determining and acquiring hardware and

software resources

Accountable for problems like poor security, poor

performance of the system

Involves in all steps of database development

92

Cont.. Further classifications of this role in big organizations having

huge amount of data and user requirement. Data Administrator (DA) Database Administrator (DBA)

Data Administrator (DA) is responsible on management of data resources. Involves in database planning, development, maintenance of standards

policies and procedures at the conceptual and logical design phases.

Database Administrator (DBA) is more technically oriented role. Responsible for the physical

realization of the database. Involves in physical design, implementation, security and integrity

control of the database.

93

Cont…

DataBase Designer (DBD) Identifies the data to be stored and choose the

appropriate structures to represent and store the data.

Should understand the user requirement and should choose how the user views the database.

Involve on the design phase before the implementation of the database system.

We have two distinctions of database designers, one involving in the logical and conceptual design and another involving in physical design.

94

Cont… Logical and Conceptual DBD

Identifies data (entity, attributes and relationship) relevant to the organization

Identifies constraints on each data Understand data and business rules in the organization Sees the database independent of any data model at conceptual

level and consider one specific data model at logical design phase.

Physical DBD Take logical design specification as input and decide how it

should be physically realized. Map the logical data model on the specified DBMS with respect

to tables and integrity constraints. (DBMS dependent designing) Select specific storage structure and access path to the database Design security measures required on the database

95

Cont…

Application Programmer and Systems Analyst

System analyst determines the user requirement and how

the user wants to view the database.

The application programmer implements these

specifications as programs; code, test, debug, document and

maintain the application program.

Determines the interface on how to retrieve, insert, update

and delete data in the database.

The application could use any high level programming

language according to the availability, the facility and the

required service.

96

Cont…

End Users

Workers, whose job requires accessing the database

frequently for various purpose. There are different group of

users in this category.

Naïve Users:

Sizable proportion of users

Unaware of the DBMS

Only access the database based on their access level and demand

Use standard and pre-specified types of queries.

97

Cont… Sophisticated Users

Are users familiar with the structure of the Database and

facilities of the DBMS.

Have complex requirements

Have higher level queries

Are most of the time engineers, scientists, business analysts, etc

Casual Users

Users who access the database occasionally.

Need different information from the database each time.

Use sophisticated database queries to satisfy their needs.

Are most of the time middle to high level managers.

98

Summary Modeling reality-entity, attributes and relationship

Three level DB architecture facilitates data independence and multiple views of the data base

Schema Vs data, instance and database state

DBMS functions and services: data storage, retrieval, update, security, integrity, transaction support….

Database languages: DDL and DML

DB environment Components: hardware, software, data, procedure, user

Database design and development stages

Roles in database environment

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End of Chapter Two

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