Data Structure is a systematic way to organize data in order to use it efficiently.

The following terms are the foundation terms of a data structure.

**Interface**− Each data structure has an interface. The interface represents the set of operations that a data structure support. An interface only provides the list of supported operations, types of parameters they can accept and return type of these operations.**Implementation**− Implementation provides the internal representation of a data structure. The implementation also provides the definition of the algorithms used in the operations of the data structure.

#### Characteristics of a Data Structure

**Correctness**− Data structures implementation should implement its interface correctly.**Time Complexity**− Running time or the execution time of operations of data structures must be as small as possible.**Space Complexity**− Memory usage of a data structure operation should be as little as possible.

#### Need for Data Structure

As applications are getting complex and data-rich, there are three common problems that applications face nowadays.

**Data Search**− Consider an inventory of 1 million(10^{6}) items of a store. If the application is to search for an item, it has to search an item for 1 million(10^{6}) items every time slowing down the search. As data grows, the search will become slower.**Processor speed**− Processor speed although being very high falls limited if the data grows to billion records.**Multiple requests**− As thousands of users can search for data simultaneously on a web server, even the fast server fails while searching the data.

To solve the above-mentioned problems, data structures come to rescue. Data can be organized in data structures in such a way that all items may not be required to be searched, and the required data can be searched almost instantly.

#### Execution Time Cases

There are three cases that are usually used to compare various data structure’s execution time in a relative manner.

**Worst Case**− This is the scenario where a particular data structure operation takes the maximum time it can take. If an operation’s worst-case time is ƒ(n) then this operation will not take more than ƒ(n) time where ƒ(n) represents the function of n.**Average Case**− This is the scene depicting the average execution time of an operation of a data structure. If an operation takes ƒ(n) time in execution, then m operations will take mƒ(n) time.**Best Case**− This is the scene depicting the least possible execution time of an operation of a data structure. If an operation takes ƒ(n) time in execution, then the actual operation may take time as the random number which would be maximum as ƒ(n).

#### Basic Terminology

**Data**− Data are values or set of values.**Data Item**− Data item refers to a single unit of values.**Group Items**− Data items that are divided into sub-items are called as Group Items.**Elementary Items**− Data items that cannot be divided are called as Elementary Items.**Attribute and Entity**− An entity is that which contains certain attributes or properties, which may be assigned values.**Entity Set**− Entities of similar attributes form an entity set.**Field**− Field is a single elementary unit of information representing an attribute of an entity.**Record**− Record is a collection of field values of a given entity.**File**− File is a collection of records of the entities in a given entity set.

Data Structures Algorithms Books: Algorithms Plus Data Structures

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