Index has two distinct meanings in computer science: an integer which identifies an array element, and a data structure which enables sublinear-time lookup. Computer science is the study of information and computation. ...

Array element identifier

When data objects are stored in an array, individual objects are selected by an index which is usually a non-negative scalar integer. Indices are also called subscripts. In computer programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... The term scalar is used in mathematics, physics, and computing basically for quantities that are characterized by a single numeric value and/or do not involve the concept of direction. ... The integers consist of the positive natural numbers (1, 2, 3, …), their negatives (−1, −2, −3, ...) and the number zero. ...

Historically, a few programming languages have identified the first element in an array using an index value of 1, but it is common practice in modern languages to identify the first element with an index value of 0. It is also a common syntactic idiom in modern programming languages to use square brackets to contain index values. If the variable sheep identifies an array, in FORTRAN the first sheep would be identified as sheep(1), while many modern computer languages would use sheep[0]. Computer code (HTML with JavaScript) in a tool that uses Syntax highlighting (colors) to help the developer see the function of each piece of code. ... Fortran (also FORTRAN) is a computer programming language originally developed in the 1950s; it is still used for scientific computing and numerical computation half a century later. ...

Support for fast lookup

Suppose a data store contains N data objects. A naive algorithm for looking up some particular object will consider each object and will thus, on average, have to examine half (for a successful lookup) or all of them; O(N) or linear time in computer-science terms. Since data stores commonly contain large numbers of objects and since lookup is a common operation, it is often desirable to improve this performance. Big O notation is a mathematical notation used to describe the asymptotic behavior of functions. ... In computational complexity, an algorithm is said to take linear time, or O(n) time, if the time it requires is proportional to the size of the input, which is usually denoted n. ...

An index is any data structure which improves the performance of lookup. There are many different data structures used for this purpose, and in fact a substantial proportion of Computer Science is devoted to the design and analysis of index data structures. There are complex design trade-offs involving lookup performance, index size, and index update performance. Many index designs exhibit logarithmic (O(log(N)) lookup performance and in some applications it is possible to achieve flat (O(1)) performance. Big O notation is a mathematical notation used to describe the asymptotic behavior of functions. ... Big O notation is a mathematical notation used to describe the asymptotic behavior of functions. ...

All database software includes indexing technology in the interests of improving performance. See Index (database). A database is an organized collection of data. ... An index is a feature in a database that allows quick access to the rows in a table. ...

One specific and very common application is in the domain of information retrieval, where the application of a full-text index enables rapid identification of documents based on their textual content. Information retrieval (IR) is the art and science of searching for information in documents, searching for documents themselves, searching for metadata which describe documents, or searching within databases, whether relational stand alone databases or hypertext networked databases such as the Internet or intranets, for text, sound, images or data. ... A search index, or more precisely a full-text index, is the database which a full-text search engine uses to respond to the query issued by the user. ...