post fix expression

Infix Postfix Prefix Notes A * B + C / D A B * C D / + + * A B / C D multiply A and B, divide C by D, add the results A * (B + C) / D A B C + * D / / * A + B C D add B and C, multiply by A, divide by D A * (B + C / D) A B C D / + * * A + B / C D divide C by D, add B, multiply by A

Read More

data structure 2nd sessional course

Sessional course data structure:

v  Double link list( insertion , deletion , display)

v  Circular link list ( insertion , deletion , display)

v  Stack ( insertion , deletion , display)

v  Queue ( insertion , deletion , display)

v  Expression evaluation/polish notation( infix,prefix,postfix)e.g table from diagram

v  Tree(theory)

v  Tree traversial.

Read More

Cardinality of Relationships

Cardinality is the number of entity instances to which another entity set can map under the relationship. This does not reflect a requirement that an entity has to participate in a relationship. Participation is another concept.
One-to-one: X-Y is 1:1 when each entity in X is associated with at most one entity in Y, and each entity in Y is associated with at most one entity in X.
One-to-many: X-Y is 1:M when each entity in X can be associated with many entities in Y, but each entity in Y is associated with at most one entity in X.
Many-to-many: X:Y is M:M if each entity in X can be associated with many entities in Y, and each entity in Y is associated with many entities in X (“many” =>one or more and sometimes zero)
 

Read More

Keys in DBMS

Super key: An attribute or set of attributes that uniquely identifies an entity–there can be many of these
Composite key:A key requiring more than one attribute

Candidate key: a superkey such that no proper subset of its attributes is also a superkey (minimal superkey – has no unnecessary attributes)

Primary key: The candidate key chosen to be used for identifying entities and accessing records.  Unless otherwise noted “key” means “primary key”

Alternate key: A candidate key not used for primary key
Secondary key: Attribute or set of attributes commonly used for accessing records, but not necessarily unique
Foreign key: An attribute that is the primary key of another table and is used to establish a relationship with that table where it appears as an attribute also.

Read More

Entities and Attributes

Entity Type:It is a set of similar objects or a category of entities that are well defined

• A rectangle represents an entity set
• Ex: students, courses
• We often just say “entity” and mean “entity type”

Attribute:It describes one aspect of an entity type; usually [and best when] single valued and indivisible (atomic)

• Represented by oval on E-R diagram
• Ex: name, maximum enrollment

Types of Attribute:

Simple and Composite Attribute

Simple attribute that consist of a single atomic value.A simple attribute cannot be subdivided. For example the attributes age, sex etc are simple attributes.

A composite attribute is an attribute that can be further subdivided. For example the attribute ADDRESS can be subdivided into street, city, state, and zip code. 

Simple Attribute: Attribute that consist of a single atomic value.

Example: Salary, age etc

Composite Attribute  : Attribute value not atomic.
Example :   Address  :  ‘House_no:City:State
Name      :  ‘First Name: Middle Name: Last Name’ 

Single Valued and Multi Valued attribute

A single valued attribute can have only a single value. For example a person can have only one ‘date of birth’, ‘age’ etc. That is a single valued attributes can have only single value. But it can be simple or composite attribute.That is ‘date of birth’ is a composite attribute , ‘age’ is a simple attribute. But both are single valued attributes.

Multivalued attributes can have multiple values. For instance a person may have multiple phone numbers,multiple degrees etc.Multivalued attributes are shown by a double line connecting to the entity in the ER diagram.

Single Valued Attribute: Attribute that hold a single value
Example1: Age
Exampe2: City
Example3:Customer id

Multi Valued Attribute: Attribute that hold multiple values.
Example1: A customer can have multiple phone numbers, email id’s etc
Example2: A person may have several college degrees

Stored and Derived Attributes

The value for the derived attribute is derived from the stored attribute. For example ‘Date of birth’ of a person is a stored attribute. The value for the attribute ‘AGE’ can be derived by subtracting the ‘Date of Birth’(DOB) from the current date. Stored attribute supplies a value to the related attribute.

Stored Attribute: An attribute that supplies a value to the related attribute.
Example: Date of Birth

Derived Attribute: An attribute that’s value is derived from a stored attribute.
Example : age, and it’s value is derived from the stored attribute Date of Birth.

Read More

Concepts of Entity Relationship Diagram( ER diagram)

Entity Relationship Model:

An Entity – Relationship model (ER model) is an abstract way to describe a database. It is a visual representation of different data using conventions that describe how these data are related to each other.
There are three basic elements in ER models:

• Entities are the “things” about which we seek information.
• Attributes are the data we collect about the entities.
• Relationships provide the structure needed to draw information from multiple entities.

Symbols used in E-R Diagram:

• Entity – rectangle
• Attribute -oval
• Relationship – diamond
• Link - line

                                                                                             

Read More

C++ Double Ended Queues

Constructors	create new deques
Operators	compare and assign deques
assign()	set the values of the deque
at()	returns a specific element
back()	returns the last element
begin()	returns an iterator to the first element
clear()	remove all elements
empty()	true if the deque is empty
end()	returns an iterator to the end of the queue
erase()	removes an element
front()	returns the first element
get_allocator()	returns the deque's allocator
insert()	insert elements into the deque
max_size()	returns the maximum elements that the deque can hold
pop_back()	removes the last element
pop_front()	removes the first element
push_back()	add an element to the end of the deque
push_front()	add an element to the front of the deque
rbegin()	returns a reverse iterator to the end of the deque
rend()	returns a reverse iterator to the beginning of the deque
resize()	change the size of the deque
size()	return the number of elements in the deque
swap()	swap one deque with another

Read More

HEC LPTOP VALIDATION LINK FOR BS STUDENTS

 

laptop validation for bs by hec

Read More