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.

Explain different database models.

q)Explain different database models.

ans:-

Database model:-A database model or database schema is the structure or format of a database, described in a formal language supported by the database management system.

There are many database models. Let's understand some of the models.

Hierarchical model:-

Hierarchical database is a model in which data is organized into a tree-like structure. In this,

• Data is organized like a family tree or organization chart
• The parent record can have multiple child records – child records can only have one parent
• Pointers link each parent record with each child record
• Complex and difficult to maintain

This structure allows one 1:N relationship between two types of data. This structure is very efficient to describe many relationships in the real world; recipes, table of contents, ordering of paragraphs/verses,

       Example:

We can see here a parent node with many branches called children.Each child has their own record with furhher informations.In given diagram, the first record has name “Ram” with street “Baneshwor” and city named kathmandu. It is further linked to its balance id and amount. In same fashion all others records have, they all are related or linked to  their id and amount. We can see records’ arrangement in tree like format.

Advantages:-   1) easiest model of database.

                      2) Searching is fast if parent is known.

                      3) supports one to many relationship.

Disadvantages:        1) old and outdated one.

                            2) Can not handle many to many relationships.

                                3) More redundancy.

Network model:-The network model organizes data using two fundamental constructs, called records and sets.        The Network Model

1. Data are represented by collections of records.
2. Relationships among data are represented by links.
3. Organization is that of an arbitrary graph.
4. Figure  shows a sample network database that is the equivalent of the relational database of Figure ??

eg.

We have taken same example as mentioned above.but the records are arranged in graph like structure. In this we do not use concept of child /parent.In given diagram the records are linked to each other with a solid line as it is in hierarchical. Two records namely Ramesh and Hary are linked to two balance id and amounts.

Advantages:- 1) more flexible due to many to many relationship.

                    2) Reduction of redundancy.

                    3) Searching is very fast.

Disadvantages:-   1) very complex.

                                2) Needs long and complex programs.

                                3) Less security

Relational model: - Three key terms are used extensively in relational database models: relations, attributes, and domains. A relation is a table with columns and rows. The named columns of the relation are called attributes, and the domain is the set of values the attributes are allowed to take.

The basic data structure of the relational model is the table, where information about a particular entity is represented in columns and rows. Thus, the "relation" in "relational database" refers to the various tables in the database; a relation is a set of tuples.So,

Relational databases

• Data is organized into two-dimensional tables, or relations
• Each row is a tuple (record) and each column is an attribute (field)
• A common field appears in more than one table and is used to establish relationships
• Because of its power and flexibility, the relational database model is the predominant design approach

name	street	city	id no.	balance
RAm	Thapagaun	KTm	00321	Rs. 900087
ekan	BAneshwor	Pokhara	008	Rs.45666
Hary	Kalanki	Ktm	9870	Rs. 65799
Sam	Koteshwor	Ktm	7890	Rs. 5600
Kale	Kalnki	Ktm	456	Rs. 65400

In this table we have used different concept like field (each column),record (each row). Each row gives us a complete information. If we have many tables then we relate them for data extractions,this is called relationship between tables.Apart from these, we also use other concept like,primary key,foreign key,Entity etc.

Explain system designing tools.

q)Explain system designing tools.
ans:-

Systems Design: In this phase we start design of proposed new system.It describes desired features and operations in detail, including screen layouts, business rules, process diagrams, pseudo code and other documentation. We can use two designing methods namely logical (what is required for IS) and physical (how to achieve requirements). At first we design logical and then it is converted into physical design. A prototype should be developed during the logical design phase if possible. The detailed design phase modifies the logical design and produces a final detailed design, which includes technology choices, specifies a system architecture, meets all system goals for performance, and still has all of the application functionality and behavior specified in the logical design.

          This design can carry following activities:

• Defining precisely the required system output
• Determining the data requirement for producing the output
• Determining the medium and format of files and databases
• Devising processing methods and use of software to produce output

We can use several tools while designing. They are: Algorithm, Flowchart, Pseudo code, etc. Let’s see in detail about some of these all designing tools.

I) Algorithm:

An algorithm is an effective method or a tool for solving a problem using a finite sequence of well organized instructions. Algorithms are used for calculation, data processing, and many other fields.

                                  Each algorithm is a list of well-defined instructions for completing a task. Starting from an initial state, the instructions describe a computation that proceeds through a well-defined series of successive states, eventually terminating in a final ending state. For example,

-->start

-->read a no. x

-->read a no. y

→ let sum=x+y

-->display sum

-->stop

                           II) Flowchart:- It is a common type of diagram or picture, that represents an algorithm or process, showing the steps as boxes of various kinds, and their order by connecting these with arrows. Or simply we can say a graphical representation of algorithm. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields. Some symbols used in flowcharts are Oval, parallelogram, rectangle, flowline, annotation etc. different symbols have different meanings. For example,

           

                                    

Pseudo Code:

Pseudo-Code is simply a numbered list of instructions to perform some task. Here Pseudo means fake. So it is a fake code which we use to convert algorithms. In this we use many English words or verbs like START/BEGIN, DO, WHILE, HALT,STOP,INITIALIZE etc, Any case can be used. Writing Pseudocode is just like reading a story. So it’s easy to write and understand. For example,

BEGIN

GET GRADE

IF student's grade is greater than or equal to 80

      Print "passed in distinction"

ELSE

      Print "other division"

HALT

Who is system analyst? Explain his/her skills to be with.

q)Who is system analyst? Explain his/her skills to be with.
ans:-
system analyst:-

The persons who perform above task/system analysis,design and implementation activity is know as system analyst. Somewhere we say or call by names like business engineer, business analyst etc. The work of system analyst who designs an information system is just same as an architect of a house. They work as facilitators of the development of information systems and computer applications.

skill to be with:-

following are the skills of system analyst.

1) Analytical skill:- Analytical skill is the ability to visualize, articulate (express), solve complex problems and concepts, and make decisions that make sense based on available information. Such skills include demonstration of the ability to apply logical thinking to gathering and analyzing information, designing and testing solutions to problems, and formulating plans.

2) Technical skill: Many aspects of the job of system analysts are technically oriented. In order to develop computer based IS (information systems), system analyst must understand information technologies, their potentials and their limitations. A system analyst needs technical skills not only to perform tasks assigned to him but also to communicate with other people with whom s/he works in system development. The technical knowledge of SA must be updated from time to time. S/he should be familiar with technologies such as:

                                >Micro/mini/mainframe computers, workstations

                             >Programming language

                    >Operating systems, database and file management systems, data communications standard system development tools and environments, decision support systems.

3)Managerial skill:-Management in all business is the act of getting people together to accomplish desired goals and objectives. This skill comprises planning, organizing, staffing, leading or directing, and controlling an organization (a group of one or more people or entities) or effort for the purpose of accomplishing a goal.

4)Interpersonal skill:-

Interpersonal skills are the life skills we use everyday to communicate and interact with other people, both individually and in groups. It includes

1. verbal communication
2. non-verbal communication
3. listening skills
4. problem solving
5. decision making
6. assertiveness (Communicating our values, ideas, beliefs, opinions, needs and wants freely.

Who is system analyst? Explain his/her roles.

q)Who is system analyst? Explain his/her roles.

ans:-
System analyst:-

The persons who perform above task/system analysis,design and implementation activity is know as system analyst. Somewhere we say or call by names like business engineer, business analyst etc. The work of system analyst who designs an information system is just same as an architect of a house. They work as facilitators of the development of information systems and computer applications.

His/her roles:-

Defining Requirement: It's very difficult duty of analyst to understand user's problems as well as requirements. some techniques like interview, questioning, surveying, data collection etc have to be used. The basic step for any system analyst is to understand the requirements of the users.

Prioritizing Requirements: Number of users use the system in the organization. Each one has a different requirement and retrieves different information and in different time. For this the analyst must have good interpersonal skill, convincing power and knowledge about the requirements and setting them in proper order of all users.

Gathering Facts, data and opinions of Users: After determining the necessary needs and collecting useful information the analyst starts the development of the system with active cooperation from the users of the system. Time to time, the users update the analyst with the necessary information for developing the system. The analyst while developing the system continuously consults the users and acquires their views and opinions.

Evaluation and Analysis: Analyst analyses the working of the current information system in the organization and finds out extent to which they meet user's needs. on the basis of facts,opinions, analyst finds best characteristic of new system which will meet user's stated needs.

Solving Problems: Analyst is actually problem solver. An analyst must study the problem in depth and suggest alternate solutions to management. Problem solving approach usually has steps: identify the problem, analyse and understand the problem, identify alternate solutions and select best solution.

Drawing up Specifications: The analyst must draw certain specifications which will be useful for the manager. The key duty of system analysis is to obtain the functional specification of the system to be designed. The specification must be non-technical so that users and managers understand it. The specification must be precise and detailed for implementers.

Designing system:- Once accepted the specification, the analyst starts to design system. The design must be understandable to the system implementer. The design must be modular to accommodate changes easily. There must be a good knowledge of latest tools and how to use them in system with testing idea.