Explain about LAN topologies.

q)Explain about LAN topologies.

ans:-

Topology:

When we go for networking, we connect some computers in particular layout or design. This design or pattern of connection is called topology.

There are many types;

Bus topology:

A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable.

Fig. 1. Linear Bus topology

Advantages of a Linear Bus Topology

• Installation is easy and cheap to connect a computer or peripheral to a linear bus.
• Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

• Entire network shuts down if there is a break in the main cable.
• Difficult to identify the problem if the entire network shuts down.
• Not meant to be used as a stand-alone solution in a large building.

Star topology:-

• A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator (See fig. 2).
• Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network.
• It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

              Fig. 2. Star topology

Advantages of a Star Topology

• Easy to install and wire.
• No disruptions to the network when connecting or removing devices.
• Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

• Requires more cable length than a linear topology.
• If the hub, switch, or concentrator fails, nodes attached are disabled.

Mesh topology

• The mesh topology incorporates a unique network design in which each computer on the network connects to every other, creating a point-to-point connection between every device on the network. The purpose of the mesh design is to provide a high level of redundancy.
• It needs/uses n(n-1)/2 channels(paths) and n-1 input/ output ports.
• If one network cable fails, the data always has an alternative path to get to its destination. Figure 6 shows the mesh topology.
• As you can see from Figure 6, the wiring for a mesh network can be very complicated.
• It is used mostly in telephone network.This allows computer to balance the load by providing alternative paths. It creates a redundant point-to-point network connection between only specific network devices.

Figure 6. Mesh topology.

Advantages	Disadvantages
Provides redundant paths between devices	Requires more cable than the other LAN topologies.
The network can be expanded without disruption to current users.	more devices needed.

Explain about DBA.(database administrator)

Explain about DBA.

ans:-

A database administrator (DBA) is a person/s who is/are responsible for the environmental aspects/activities related to database. The role of a database administrator has changed according to the technology of database management systems (DBMSs) as well as the needs of the owners of the databases.

                Duties:

1. Installation of new software.

2. Configuration of hardware and software with the system administrator

3. Security administration

4. Data analysis

5. Database design (preliminary

6. Data modeling and optimization

7. Responsible for the administration of existing enterprise databases and the analysis, design, and creation of new databases

Explain about database and DBMS.

Explain about database and DBMS.

ans:-

Database: - Database is a collection of data for one or more multiple uses in very well organized format.

Or

Simply well organized collection of data is database.

One way of classifying databases involves the type of content, for example: bibliographic, full-text, numeric, and image. Databases consist of software-based "containers" that are structured to collect and store information so users can retrieve, add, update or remove such information in an automatic fashion. Database programs are designed for users so that they can add or delete any information needed. The structure of a database is tabular, consisting of rows and columns of information.

Advantages

• Reduced data redundancy
• Improved data security
• Reduced data entry, storage, and retrieval costs
• Facilitated development of new applications program
• improved data integrity (integrity:data should be accurate & accurate; it is done by providing some checks
• multiple users.

  Disadvantages

• Database systems are complex, difficult, and time-consuming to design
• Substantial hardware and software start-up costs
• Initial training required for all programmers and users

Database Management System (DBMS):-It’s a set of computer programs that controls the creation, maintenance, and the use of the database with computer as a platform or of an organization and its end users.

            A DBMS is a system software package that helps the use of integrated collection of data records and files known as databases. It allows different user application programs to easily access the same database. DBMSs may use any of a variety of database models, such as the network model or relational model. In large systems, a DBMS allows users and other software to store and retrieve data in a structured way. Instead of having to write computer programs to extract information, user can ask simple questions in a query language.

             Its roles can be listed as given below.

1. provides an interface to the user as well as to application

2. lets user to create,maintain databases.

3. provides high integrity and security to its data.

4. provides sharing facility to many users.

5. provides relationships between tables.

6. provides access level to different users.

7. maintains integrity,consistency of data etc

Disadvantages:

1.initial setup is expensive

2. training to staffs has to be provided

3.database failures.

4.data conversion( computer file into database file which takes more time)

Explain E-R diagram with example.

Explain E-R diagram with example.

ans:-

The Entity-Relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects. An entity is a “thing” or “object” in the real world that is distinguishable from other objects. For example, each person is an entity, and bank accounts can be considered as entities.

Entities are described in a database by a set of attributes. For example, the attributes account-number and balance may describe one particular account in a bank, and they form attributes of the account entity set. Similarly, attributes customer-name, customer-street address and customer-city may describe a customer entity.

A relationship is an association among several entities. For example, a depositor relationship associates a customer with each account that she has. The set of all entities of the same type and the set of all relationships of the same type are termed an entity set and relationship set, respectively.

The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram, which is built up from the following components:

• Rectangles, which represent entity sets
• Ellipses, which represent attributes.
• Diamonds, which represent relationships among entity sets.
• Lines, which link attributes to entity sets and entity sets to relationships.

for example,

E-R can have following types.

one-to-one

one-to-many

many-to-many

Differentiate between centralized and distributed database system.

Differentiate between centralized and distributed database system.

ans:-

Following are differences between distributed and centralized database system.

Centralized system	Distributed System
1.Job is centralized.	1.Job is distributed.
2. Can not process if main server fails.	2. Can still be if a server fails;processing can be done by other servers.
3. Security is given to one machine.	3.Security is given to all.
4.No need to have network for communication.	4 Needs communication channel between all.
5.Not so expensive to set up.	5.It’s expensive to set up.
6.Data speed is comparatively fast.	6.Data speed is slow.
7.Low quality performance. Diagrammatically it can be shown as	7.High quality performance. Diagrammatically it can shown

Explain about data security.

Explain about data security.

ans:-

Data security:-

        It simply says protection of data /information contained in database against unauthorized access, modification or destruction. The main condition for database security is to have “database integrity’ which says about mechanism to keep data in consistent form. Besides these all, we can apply different level of securities like:

1. Physical: - says about sites where data is stored must be physically secured.
2. Human: - an authorization is given to user to reduce chance of any information leakage or manipulation.
3. Operating system: must be taken a foolproof operating system regarding security such that no weakness in o.s.
4. Network: - since database is shared in network so the software level security for database must be maintained.
5. Database system: - the data in database needs final level of access control i.e. a user only should be allowed to read and issue queries but not should be allowed to modify data.

Etc.

Explain about data integrity.

q)Explain about data integrity.

ans:-

Database integrity:

It means the correctness and consistency of data. It is another form of database protection.

Put simply, data integrity is the assurance that data is consistent and correct.

Data integrity is normally enforced in a database system by a series of integrity constraints or rules.

         Three types of integrity constraints are an inherent part of the relational data model: entity integrity, referential integrity

Entity integrity concerns the concept of a primary key. Entity integrity is an integrity rule which states that every table must have a primary key and that the column or columns chosen to be the primary key should be unique and not null. It means the primary key’s data must not be missing in table/s.

   or

The entity integrity is a constraint on primary key value. It states that any attribute of a primary key cannot contain null value. If primary key contains null value, it is not possible to uniquely identify a record in a relation. Entity integrity ensures that it should be easy to identify each entity in the database.

Referential integrity concerns the concept of a foreign key. The referential integrity rule states that any foreign key value can only be in one of two states. The usual state of affairs is that the foreign key value refers to a primary key value of some table in the database. Occasionally, and this will depend on the rules of the business, a foreign key value can be null. In this case we are explicitly saying that either there is no relationship between the objects represented in the database or that this relationship is unknown.

Or

Referential Integrity

Referential integrity ensures that the relationship between the primary key (in a referenced table) and the foreign key (in each of the referencing tables) is always maintained. The maintenance of this relationship means that:

• A row in a referenced table cannot be deleted, nor can the primary key be changed, if a foreign key refers to the row. For example, you cannot delete a customer that has placed one or more orders.
• A row cannot be added to a referencing table if the foreign key does not match the primary key of an existing row in the referenced table. For example, you cannot create an order for a customer that does not exist.

Domain Integrity

Domain (or column) integrity specifies the set of data values that are valid for a column and determines whether null values are allowed. Domain integrity is enforced by validity checking and by restricting the data type, format, or range of possible values allowed in a column.