1. What is a Database? A database is any collection of data.
A DBMS is a software system designed to maintain a database.
We use a DBMS when
there is a large amount of data
security and integrity of the data are important
many users access the data concurrently

2. Chararacteristic Of Database Approach
Concurrent Use
Structured Data
Separation of Data and Applications
Data Integrity
Transactions
Data Persistence
Data Views

3. Concurrent Use
A database system allows several users to access the database concurrently. Answering different questions from different users with the same (base) data is a central aspect of an information system.  Such concurrent use of data increases the economy of a system. Data capturing and data storage is not redundant, the system can be operated from a central control and the data can be updated more efficiently

4. Structured and Described Data
A fundamental feature of the database approach is that the database system does not only contain the data but also the complete definition and description of these data. These descriptions are basically details about , the structure, the type and the format of all data and, additionally, the relationship between the data. This kind of stored data is called metadata ("data about data"). 
Structured Data:Data is called structured if it can be subdivided systematically and linked.

5. Separation of Data and Applications
 software application does not need any knowledge about the physical data storage like encoding, format, storage place, etc. It only communicates with the management system of a database (DBMS) via a standardised interface with the help of a standardised language like SQL. The access to the data and the metadata is entirely done by the DBMS. In this way all the applications can be totally separated from the data. Therefore database internal reorganisations or improvement of efficiency do not have any influence on the application software.

6. Data Integrity
Data integrity ensures the quality and the reliability of the data of a database system.Data integrity includes also the protection of the database from unauthorized access (confidentiality) and unauthorized changes. . A DBMS should bring only correct and consistent data into the database. Additionally, correct transactions ensure that the consistency is maintained during the operation of the system.
An example for inconsistency would be if contradictory statements were saved in the same database.

7. Transactions
A transaction is a bundle of actions which are done within a database to bring it from one consistent state to a new consistent state. In between the data are inevitable inconsistencies.  A transaction is atomic, which means it cannot be divided up any further. Within a transaction all or none of the actions need to be carried out. Doing only a part of the actions would lead to an inconsistent database state.

8. Data Persistence
Data persistence means that in a DBMS all data is maintained as long as it is not deleted explicitly. The life span of data needs to be determined directly or indirectly be the user and must not be dependent on system features. Additionally data once stored in a database must not be lost.  Changes of a database which are done by a transaction are persistent. When a transaction is finished even a system crash cannot put the data in danger.

9. Data Views
Typically, a database has several users and each of them, depending on access rights and desire, needs an individual view of the data (content and form). Such a data view can consist of a subset of the stored data or from the stored data derived data (not explicitely stored).

10. Advantages of Using the Database Approach
More information from given data
Ad hoc queries can be performed
Redundancy can be reduced
Inconsistency can be avoided
Security restriction can be applied
Data independence
more cost-effective: reduced development time, flexibility, economies of scale

11. Advantages of Using the Database Approach – 3.
Providing backup and recovery services.
Providing multiple interfaces to different classes of users.
Representing complex relationships among data.
Enforcing integrity constraints on the database.
Drawing Inferences and Actions using rules

12. Disadvantages of Using the Database Approach
Expensive
hardware, software, personnel, processing overhead, operating cost , etc.
DBMS generality & overhead
=> performance issue
Increased vulnerability to failure
Recovery is more complex

13. Database System Architecture and data Independence

14. Three-Schema Architecture
Proposed to support DBMS characteristics of:
Program-data independence.
Support of multiple views of the data.

15. Three-Schema Architecture
Defines DBMS schemas at three levels:
Internal schema at the internal level to describe physical storage structures and access paths. Typically uses a physical data model.
Conceptual schema at the conceptual level to describe the structure and constraints for the whole database for a community of users. Uses a conceptual or an implementation data model.
External schemas at the external level to describe the various user views. Usually uses the same data model as the conceptual level.

16. The three­schema architecture

17. Three-Schema Architecture
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.

18. Data Independence Logical Data Independence:
Data independence is defined as the capacity to change the schema at one level of database s/m with out having to change the schema at next higher level.
Types of DI:
Logical Data Independence: 
The capacity to change the conceptual schema without having to 
change the external schemas and their associated application 
programs.
Physical Data Independence:
The capacity to change the internal schema without having to 
change the conceptual schema.
For example, the internal schema may be changed when certain file 
structures are reorganized to improve Database performance

19. Data Independence
When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independence. The higher-level schemas themselves are unchanged. Hence, the application programs need not be changed since they refer to the external schemas.

20. Database Model
A database model is a type of data model that determines the logical structure of a database and fundamentally determines in which manner data can be stored, organized, and manipulated.
Common data models for databases include:
Hierarchical database model
Network model
Relational model
Entity–relationship model
Enhanced entity–relationship model
Object model

21. Hierarchical DB model Logically represented by an upside down TREE
SALIENT FEATURES
Logically represented by an upside down TREE
Each parent can have many children
Each child has only one parent
The top layer is perceived as the parent of the segment directly beneath it.
The segments below other segments are the children of the segment above them.

22. Hierarchical DB model

23. Advantages Conceptual simplicity Data independence
Efficiency dealing with a large database

24. Disadvantages Complex implementation
Difficult to manage and lack of standards
Lacks structural independence
Applications programming and use complexity
Implementation limitations (no M:N relationship)

25. Network DB model
Developed in mid 1960s as part of work of CODASYL (Conference on Data Systems Languages)
The network model has greater flexibility than the hierarchical model for handling complex relationships
Objective of network model is to separate data structure from physical storage, eliminate unnecessary duplication of data with associated errors and costs
The Network Database Model was created for three main purposes :
- representing a complex data relationship more effectively
- improving database performance
- imposing a database standard

26. Network DB model
Major characteristic of this database model is that it comprises of at least two record types ; the owner & the member.
An owner is a record type equivalent to the parent type in the hierarchal database model, and the member record type resembles the child type in the hierarchal model.
The network database model uses a data management language that defines data characteristics and the data structure in order to manipulate the data.

27. Network DB model
The network model contains logical information such as connectivity relationships among nodes and links, directions of links, and costs of nodes and links.

28. Advantages Simplicity Ability to handle more relationship types :
Ease of data access
Data Integrity :
Data Independence

29. Disadvantages
System Complexity : The structure of the network model is very difficult to change. This type of system is very complex
Lack of Structural independence. Any changes made to the database structure require the application programs to be modified before they can access data.

30. Relational DB model

31. Relational DB model
The relational model uses a collection of tables to represent both data and relation among the data

32. Definitions Cont.
Table, a set of rows and columns .each column cthe has a unique name
Row, a set of columns from a table reflecting a record.
Primary key, often designated pk, is 1 or more columns in a table that makes a record unique.
In the relational model ,a row is called a tuple ,a column header is called an attribute and the table is called a relation

33. Definitions Cont.
Foreign key, often designated fk, is a common column common between 2 tables that define the relationship between those 2 tables.
Foreign keys are either mandatory or optional.

34. Disadvantage
Hardware overhead : need more powerful computing hardware and data storage devices to perform RDBMS tasks

35. . Entity Relationship Model
Entity Relationship Model or ER is based on a perception of a real world that consists of a collection of basic objects called entities and relationship among these objects
The overall structure of a database can be represented graphically by E-R diagram

36. . Entity Relationship Model
Entity Relationship Model or ER is build up from the following components
Rectangle: represent the entity sets
Ellipses: represents the attributes
Diamonds: relationship among entity sets
Lines :links attributes to entity sets and entity sets to relationships

37. Entity Relationship Model
Double ellipses: which represent multi valued
Attributes
Dashed ellipses: which denote derived attributes
Double lines : which represent which represent total participates in an entity in a relationship set
Double Rectangle : which represent weak entity sets

38. Index_no

39. Object –Oriented Data Model
It is based on the object –oriented –programming language paradigms
The objects-oriented paradigm is based on the Encapsulation of data and code related to an object into a single unit , inheritance and object -identity