1. External Level : The users’ view of the database. This level
describes that
Part of the database that is relevant to each user.
2. Conceptual Level :
This level
describes what data is stored in the database and relationships among the data.
Conceptual level represents: all entities, their attributes,
and their relationship
-
The constraints on the data
-
Semantic information about the data
-
Security and integrity information
3. Internal Level: This level describes how the data is stored in the database.
- Storage space allocation for data and indexes.
- Record descriptions for storage (with stored sizes for
data items)
- Record replacement.
- Data compression and data encryption techniques.
Schema, Mappings and Instances
The overall description of the database is called database
schema. There are three types of schema external, internal and
conceptual schema.
Data Independence
+Logical
data independence: refers to external schema to changes in the conceptual
schema. Example adds or removes of new entities, attributes or relationship
without having to change existing external schema or having to rewrite the
application program.
+Physical
data independence: refers to the
conceptual schema to changes in the internal schema. Changes to the internal
schema, such as using different file organization or storage structures, using
different storage devices, modifying indexes, or hashing algorithms, should be
possible without having changed the conceptual or external schema.
Database Languages
+ Data
Definition Language (DDL) is a language that allows DBA or
users to describe and name the attributes, and relationships required for the
application, together with associated integrity and security constraints.
+ Data
Manipulation Language (DML) is a language that provides a set of operations
to support the basic data manipulations on the data help in the database. Data
manipulation operations are insertion, modification, retrieval and deletion.
Procedural DML: A language
that allow users tell the system what data is needed and exactly how to
retrieve the data.
Non-procedural DML: A language
that allows the user to state what the data is needed rather than how it is to
be retrieved.
Data Models and Conceptual Modeling
Data Model: An integrated collection of concepts for describing
and manipulating data relationships between data, and constraints on the data
in an organization.
A model is representation of real world objects and events, and their association.It is an abstraction that concentrates on the essential.
Components of data model:
1.) Structural part. consisting of a set of rules according to which database can be constructed.
2.) Manipulative part allow operations insert,delete,update and retrieve data.
3.) Set of integrity constraints to ensure the data is accurate.
Object-Based Data Models
use concepts such as entities, attributes, and relationships. Common types of object-based data model are :
+ Entity-Relationship
+ Semantic
+ Functional
+ Object-Oriented.
Record-Based Data Models
Database consists of number of fixed-format records in different types. Each record type defines a fixed number of fields, each field has fixed length. There are three principle type of record-based logical data model.
+Relational data model grouped into relations and provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries.
+Network data model
a flexible way of representing objects and their relationships. It is of the schema, viewed as a graph in which object types are nodes and relationship types are arcs
+Hierarchical data model
is a data model in which the data is organized into a tree-like structure. The structure allows representing information using parent/child relationships: each parent can have many children, but each child has only one parent (also known as a 1-to-many relationship). All attributes of a specific record are listed under an entity type.
Physical Data Models
describe how data is stored in the computer, representing information such as record structures, record orderings, and access paths.
Conceptual Modeling or Conceptual database design.
is the process of constructing a model of the information use in an enterprise that is independent of implementation details such as the target DBMS, application programs, programming languages or any other physical considerations.
Functionals of a DBMS
1.) Data Storage, retrieval, and update
A DBMS must have users ability to store, retrieve, and update data in the database.
2.) A User-accessible catalog
A DBMS must have a catalog in which descriptions of data items are stored which is accessible to users.
System catalog stores: names,types,and sizes of data items, name of relationships,name of authorized users who have access to data,usage statistic,security,audit information,redundancy and consistency.
3.) Transition support
A DBMS must have a mechanism which will ensure either that all the updates corresponding to a given transaction are made or that none of them is made.
4.) concurrency control services
A DBMS must have a mechanism to make sure the database is updated correctly when multiple users are updating the database concurrently.
5.) Recovery Services
A DBMS must have a mechanism for recovering the database when the database has damaged in anyway.
6.) Authorization Services
A DBMS must have a mechanism to ensure that only authorized users can access the database.
7.) Support for data communication
A DBMS must be capable of integrating with communication software.
8.) Integrity Services.
A DBMS must have to ensure that both the data in database and changes to the data follow certain rules.
9.) Services to promote data independence
A DBMS must include facilities to support the independence of programs from the actual structure of the database.
10.) Utility Services
A DBMS should provide a set of utility services.
Components of DBMS
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Multi-User DBMS Architectures.
1.) Teleprocessing : There is one computer with a single central processing unit (CPU) and number of terminals like pictures.
2.) File-Server Architecture
As the file-server has no knowledge of SQL, the DBMS has to request the files corresponding to the Branch and staff relations from the file-server, rather than just the staff names that satisfy the query.
A model is representation of real world objects and events, and their association.It is an abstraction that concentrates on the essential.
Components of data model:
1.) Structural part. consisting of a set of rules according to which database can be constructed.
2.) Manipulative part allow operations insert,delete,update and retrieve data.
3.) Set of integrity constraints to ensure the data is accurate.
Object-Based Data Models
use concepts such as entities, attributes, and relationships. Common types of object-based data model are :
+ Entity-Relationship
+ Semantic
+ Functional
+ Object-Oriented.
Record-Based Data Models
Database consists of number of fixed-format records in different types. Each record type defines a fixed number of fields, each field has fixed length. There are three principle type of record-based logical data model.
+Relational data model grouped into relations and provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries.
+Network data model
a flexible way of representing objects and their relationships. It is of the schema, viewed as a graph in which object types are nodes and relationship types are arcs
+Hierarchical data model
is a data model in which the data is organized into a tree-like structure. The structure allows representing information using parent/child relationships: each parent can have many children, but each child has only one parent (also known as a 1-to-many relationship). All attributes of a specific record are listed under an entity type.
Physical Data Models
describe how data is stored in the computer, representing information such as record structures, record orderings, and access paths.
Conceptual Modeling or Conceptual database design.
is the process of constructing a model of the information use in an enterprise that is independent of implementation details such as the target DBMS, application programs, programming languages or any other physical considerations.
Functionals of a DBMS
1.) Data Storage, retrieval, and update
A DBMS must have users ability to store, retrieve, and update data in the database.
2.) A User-accessible catalog
A DBMS must have a catalog in which descriptions of data items are stored which is accessible to users.
System catalog stores: names,types,and sizes of data items, name of relationships,name of authorized users who have access to data,usage statistic,security,audit information,redundancy and consistency.
3.) Transition support
A DBMS must have a mechanism which will ensure either that all the updates corresponding to a given transaction are made or that none of them is made.
4.) concurrency control services
A DBMS must have a mechanism to make sure the database is updated correctly when multiple users are updating the database concurrently.
5.) Recovery Services
A DBMS must have a mechanism for recovering the database when the database has damaged in anyway.
6.) Authorization Services
A DBMS must have a mechanism to ensure that only authorized users can access the database.
7.) Support for data communication
A DBMS must be capable of integrating with communication software.
8.) Integrity Services.
A DBMS must have to ensure that both the data in database and changes to the data follow certain rules.
9.) Services to promote data independence
A DBMS must include facilities to support the independence of programs from the actual structure of the database.
10.) Utility Services
A DBMS should provide a set of utility services.
Components of DBMS
Multi-User DBMS Architectures.
1.) Teleprocessing : There is one computer with a single central processing unit (CPU) and number of terminals like pictures.
Disadvantage of file-server
+ Large amount of network traffice.
+ A full copy of the DBMS is required on each workstation.
+ Concurrency, recovery, and integrity control are more complex because there can be multiple DBMS accessing the same files.
Two Tier and Three Tier Client-Server Architecture
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Transaction Processing Monitors.
TP Monitor A program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for online trans-action processing.
Transaction Routing The TP Monitors can increase scalability by directing transaction to specific DBMS.
Transaction Processing Monitors.
TP Monitor A program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for online trans-action processing.
Transaction Routing The TP Monitors can increase scalability by directing transaction to specific DBMS.
Load Balancing: The
TP Monitor can balance client requests across multiple DBMS on one or more
computers by directing client service calls to the least loaded server. It can
dynamically bring in additional DBMS as required to provide necessary
performance.
Funneling in
environment with large number of users sometime users difficult logged on simultaneously
to the DBMS. The TP Monitor can establish connections with the DBMS as the
required, and can funnel user request through these connection.
Increases reliability:
TP Monitor acts as a transaction manager, performing necessary actions to
maintain consistency of the database, with the DBMS acting as a resource
manager. If the DBMS fails, the TP Monitor maybe able to resubmit the
transaction to another DBMS or can hold the transaction until the DBMS become
available again.
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