LINQ defines standard query operators that allow code written in LINQ-enabled languages to filter, enumerate, and create projections of several types of collections using the same syntax. Such collections may include arrays, enumerable classes, XML, datasets from relational databases, and third party data sources. The LINQ project uses features of version 2.0 of the .NET Framework, new LINQ-related assemblies, and extensions to the C# and Visual Basic .NET languages. Microsoft has distributed a preview release of LINQ, consisting of those libraries and compilers for C# 3.0 and Visual Basic 9. Other languages, such as F# and Nemerle, have also announced preliminary support.

A database index is a data structure that improves the speed of operations in a table. Indices can be created using one or more columns, providing the basis for both rapid random lookups and efficient ordering of access to records. The disk space required to store the index is typically less than the storage of the table (since indices usually contain only the key-fields according to which the table is to be arranged, and excludes all the other details in the table), yielding the possibility to store indices into memory from tables that would not fit into it. In a relational databasean index is a copy of part of a table. Some databases extend the power of indexing by allowing indices to be created on functions or expressions. For example, an index could be created on upper(last_name), which would only store the uppercase versions of the last_name field in the index. Another option sometimes supported is the use of "filtered" indices, where index entries are created only for those records that satisfy some conditional expression. A further aspect of flexibility is to permit indexing on user-defined functions, as well as expressions formed from an assortment of built-in functions.

Its an object that QTP uses to represent an object in our application. Each test object has one or more methods and properties that we can use to perform operations and retrieve values for that object. Each object also has a number of identification properties that can describe the object.

System.String is immutable.  System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

Relational operators must be declared in pairs.

Unary, binary, and conversion.