03 Im Uml Construction and Data Bases

8/19/2019 03 Im Uml Construction and Data Bases

1/18

Different way tostore data

24

Data types

Number and strings

Signals

Images

F i l es are a data storage entity that contain

data according to the application organization.

Binary or Text

Da t aba se s offer an organized mechanism for

storing, managing and retrieving informationthat is independent from the applications.


2/18

Databases

25

A da t a ba s e is a collection of files.

A f i l e is a collection of byte that has aname. Files are accessed by means oftheir name.

A file is further subdivided into logicaldata r e c o r d s .

A record is a collection of d a t a .

Symbol used

to indicate adatabase


3/18

There are three main components to any DB application:

A m et h o d f o r en t er i n g a n d ed i t i n g d a t a (usually data entry

screens or import functions)

A d a t a st o r a g e m ech a n i sm (a way of storing the data on thecomputer)

A r ep o r t g en er a t o r to extract and interpret information fromthe stored data


4/18

27

Data in a DB is organized in a structured way. The structure isachieved using a database model. The model that is most commonlyused today is the relational model.

There are two types of databases:

Oper a t i o n a l d a t a b a se: they are primarily used in on-line

transaction processing (OLTP) scenarios, where data is collected,modified and maintained on a daily basis.

An a l y t i ca l d a t a b a se: they are used in on-line analytical

processing (OLP) scenarios, where data is never modified and isused for example for statistical analysis.


5/18

28

D a t a a b st r a ct i o n : a data model is used to hide storage detailsand present the users with a conceptual view of the database;programs refer to the data model constructs rather than datastorage details

Su pp o r t o f m u l t i p l e v i ew s o f t h e d a t a : each user may see a

different view of the database, which describe only the data ofinterest to that user

Sh a r i n g o f d a t a e m u l t i -u ser t r a n sa ct i o n p r o cessi n g :

allowing a set of concurrent users to retrieve from and to updatethe database.


6/18

DBMS

29

DataBase Management System

(DBMS) is a software system that isused to define, create and maintaindatabases.

It assists in maintaining and utilizinglarge collections of data and also

provides various levels of accesscontrol to users.

It can be seen as a mediator betweenusers and/or applications anddatabases.


7/18

30

DBMS may have utilities software such as database designer tools,

report writers and application development tools.

Examples of DBMS are Oracle, Access, SQL server …

DBMS manage backup and recovery.

DBMS is installed on a computer that is called database server.

It can be a single or multi-user system.


8/18

31

In large organizations there is a large number of users and volume of datais high.

In this case to allow its management by several users, data is integratedand shared.

Data is kept on various database servers and with the help of computernetworks data can be transmitted from one server to another.

It is responsibility of DBMS to provide data to various users at a timeand ensure that no users can modify the same piece of data at thesame time.

Users share data but may have different levels of access to databases:some users may only be allowed to view data, others may also modifydata.

These permissions are called privileges.


9/18

32

Data Dictionary keeps all kind of information about Users

Internal structure of databases

Privileges

…


10/18

33

Single tier system.Mainframes or minicomputers were used tokeep centralized databases. Terminals were usedto access databases through DBMS

Two-tier system.

It is an example of distributed computing wheredifferent software is required for server machineand for the client machine.

This system is called Client/Server

database system. A client-server environment was common in thepreInternet days where a transactional databaseserviced users within a single company.


11/18

3434

Three-tier system.In this system a special software called

middleware is used to connect client of oneDBMS to access another DBMS.

In a distributed computing system there are many DBMS installed on differentserver machines.

Applications can access data from local and remote databases.Data is stored geographically and resides to nearer where it will be used.


12/18

35

: application programs are independent fromdetails of data storage and representation. Also data are independent fromapplications.

: security is provided bycontrolling the operations that each user may perform (privileges); dataintegrity is the result of having each datum stored only in one place (inconventional systems data are duplicated in multiple files).

: changes are often necessary to the contents of the data; because programs and data are independent, programs do not have to bemodified when physical storage changes.

: complexrequests can be handled much more rapidly then if the data were located inseparated files.


13/18

3636

: in the conventional file

processing system, every user group maintains its own files for handling its datafiles. This may lead to:

Duplication of the same data in different files

Wastage of storage space Errors may be generated when the same data are updated in different

files

Time wasted in entering data again and again

: when data are duplicated indifferent files modifications may lead to inconsistency; a DBMS contains amechanisms to avoid inconsistency.


14/18

37

: is a person (or a group of persons) who is responsible for the supervision of the database. He is responsible for givingpermission to the users by grant and revoke privileges. He is also responsible forcoordinating and monitoring its use, managing backups and recovery, and for

acquiring hardware and software resources as needed.: they are responsible for identifying the data to be

stored and for choosing the appropriate structure to represent and store the data.

: are the people who interact with the database through applicationsand utilities. There are different types of end users:

Casual end users – people that need different information each time; they uses thedatabase query language;

Native end users – they uses the same queries each time, usually by means ofapplications.

: they write programs, that make use of

databases, to handle a specific job.


15/18

38

A database model is used to explain the logical layout meaning the relationshipsamong the various parts the database consists of.

In fact data must be stored in some fashion in a file for it to be useful.

Over the past 30 years there have been three groups of logical databasemodels:

Hierarchical

Network

Relational

meaning three ways of logically perceiving the arrangement of data in the filestructure.

The relational database modeling is currently the best solution for both storage

and retrieval of data.


16/18

39

The initial solution was no virtually database model at all: the file

system (also known as flat files).The term flat file is a way of describing a simple text file, containingno structure. Flat files are not database at all.

Pre 1950

1980

The evolution of database modeling occurred when each database

model improved upon the previous one.

HIERARCHICAL model

is an inverted tree-like

structure.

1950

1990


17/18

40

NETWORK model

organizes files in a mannerthat associates each file with nnumber of other files.

1960

2000

RELATIONAL modelis a data is stored in tables (also referredto as entities). Each table has rows (alsoreferred as records) and columns (also

referred to as attributes). In this modelany table can be linked together.

1970


18/18

41

Basato su tabelle e relazioni

03 Im Uml Construction and Data Bases

Documents

Transcript of 03 Im Uml Construction and Data Bases