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Please carefully read the following instructions before attempting the assignment.

 

Deadline

Your assignment must be uploaded before or on  May 2014.

Assignment 1 is Non Graded and Marks will not be included in the final grades.

Rules for Marking

It should be clear that your assignment will not get any credit if:

1. The assignment is submitted after due date

2. The assignment is copied

3. You are supposed to submit your assignment in .doc / Docx format. Any other formats like scan    images, PDF, Zip, rar, bmp etc will not be accepted.

 

For any query please contact: CS403@vu.edu.pk

 

Objectives

The objective of this assignment is:

  • Giving the idea of entities and their attributes.

 

 

 

 

Case Study

Suppose we have a wireless ad hoc network. A wireless ad hoc network is a decentralized type of wireless network. The network is ad hoc because it does not rely on a pre existing infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks. Instead, each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity.

Nodes in the ad hoc network has unique id that identify it across the network. Each of the nodes uses a certain protocol.

Various protocols are used including aodv, dsdv, dsr etc. There are various version of a specific protocol. An ad hoc network typically refers to any set of networks where all devices have equal status on a network and are free to associate with any other ad hoc network device in link range.

Nodes in the ad hoc networks send packets to each other. Each packet has two parts namely: header and data. Header information contains source destination IP address and some other information. Every packet will leave for a certain time of period around the network called RTT (Round trip time).  Each packet is sent on one of the route based on the source destination address. There can be several hops around one route. Every route is assigned a weight based on some pre defined rule. 

Keeping in view the above scenario you are required to solve the following task(s).

 

Tasks:

In this assignment you will focus on the tasks given below:

Task#1: [Marks 15]

Identify all the Entities along with proper attributes.

You have to perform all these steps given above in your solution file.

 

Good Luck

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Replies to This Discussion

Identify Key Attributes

Candidate Key
A candidate key is one or more attribute that uniquely identifies an entity. Every entity in relational database must have at least one candidate key but it is possible that some may have two or more. For example, his social security number, employee number or driver license number may identify an employee. All of them are considered candidate keys for an employee.
Primary Key
A primary key is an attribute, or set of attributes, that allows each information for an entity to be uniquely identified. Every entity in a relational database must have a primary key. For example, if an employee has attribute such as name, phone number, employee number, social security number, department name etc., then the employee number or social security number can be used as a primary key. However, one cannot use both attributes as a primary key since one attribute by itself can identify the employee. Using both candidate key sas the primary key could cause redundancy and increase error in data. 

Note: For any given relationship or entity, primary key is one of the candidate keys and the remainder (if any) are called alternate keys.
Foreign Key
The entities are related to each other through foreign keys. uA foreign key references a particular attribute of an entity containing the corresponding primary key. For example, an employee entity with employee number as its primary key for an employee and department entity with department number as its primary key for department information can be related to each other through employee number. Therefore, employee number will be a foreign key for department entity where as the employee number will be a primary key for the employee entity.

Identify entities and relationships

Once the requirements have been defined, the next step is to identify the entities, its attributes and the relationships between entities.

Identify entities
uFor the list of activities, identify the subject areas you need to maintain information about. These will become tables. An entity may be an object with a physical existence - a particular person, car, house, or employee - or it may be an object with a conceptual existence - a company, a job, or a university course. 

For example, to develop a company's database for maintaining information on employees, the application should be able to store and provide data on employee such as when was the employee was hired; is the employee still with the company; if the employee has left the company when did he leave the company; which department does employee work for; who is his/her manager; what is his/her skill level etc. In this example, the entities are company, department, employee, manager.
Identify Attributes
An Attribute is a property that describes an entity. In the above example, the employee is the entity and employee’s name, age, address, salary and job etc are the attribute. 
Identify Relationships
Next step is to determine the relationships between the entities. Give each the relationship a name. In the above example, there is a relationship between departments and employees, so we will name this relationship dept_employee. Type of relationship.

Thanks U Sir 

thnxxxx

Friends Database Management System men Entities aur Attributes ko asaani se samjhnay ke liye aur es assignment ko hal karnay ke liye ye slide zarur dekhen its very easy .....

http://infolab.stanford.edu/~ullman/fcdb/slides/slides1.pdf

Thank you.

thanks

Kerna kyia hy ?? 

Check this file..it’s much helpful to solve this assignment

Attachments:

Thanks for sharing sir 

Entities

In a database model, each object that you wish to track in the database is known as an entity. Normally, each entity is stored in a database table and every instance of an entity corresponds to a row in that table. In an ER diagram, each entity is depicted as a rectangular box with the name of the entity contained within it.

For example, a database containing information about individual people would likely have an entity called Person. This would correspond to a table with the same name in the database and every person tracked in the database would be an instance of that Person entity and have a corresponding row in the Person table. Database designers creating an E-R diagram would draw the Person entity using a shape similar to this:

They would then repeat the process to create a rectangular box for each entity in the data model.
Attributes

Of course, tracking entities alone is not sufficient to develop a data model. Databases contain information about each entity. This information is tracked in individual fields known as attributes, which normally correspond to the columns of a database table.

For example, the Person entity might have attributes corresponding to the person's first and last name, date of birth, and a unique person identifier. Each of these attributes is depicted in an E-R diagram as an oval, as shown in the figure below:

this is a sample ER Diagram now read the scenario carefully and by using this shapes make ur Assigment 

Best of luck !!

Thank u so much 

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