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Data type

-> A data type (or datatype) in programming languages is a set of values and the operations on those values.

Classes of data types:

1. Abstract Data Type

In computing, an abstract data type (ADT) or abstract data structure is a mathematical model for a certain class of data structures that have similar behavior; or for certain data types of one or more programming languages that have similar semantics. An ADT is defined indirectly, only by the operations that may be performed on it and by mathematical constraints on the effects (and possibly cost) of those operations .

For example, an abstract stack data structure could be defined by two operations: push, that inserts some data item into the structure, and pop, that extracts an item from it; with the constraint that each pop always returns the most recently pushed item that has not been popped yet. When analyzing the efficiency of algorithms that use stacks, one may also specify that both operations take the same time no matter how many items have been pushed into the stack, and that the stack uses a constant amount of storage for each element.

ADTs are purely theoretical entities, used (among other things) to simplify the description of abstract algorithms, to classify and evaluate data structures, and to formally describe the type systems of programming languages. However, an ADT may be implemented by specific data types or data structures, in many ways and in many programming languages; or described in a formal specification language. ADTs are often implemented as modules: the module's interface declares procedures that correspond to the ADT operations, sometimes with comments that describe the constraints. This information hiding strategy allows the implementation of the module to be changed without disturbing the client programs. Abstract data types are also an important conceptual tool in object-oriented programming and design by contract methodologies for software development.

The name "abstract data type" apparently was coined by researches in software engineering and programming language design; while "abstract data structure" was coined by researchers in data structures and algorithms.

^2. Algebraic data types

, an algebraic data type (sometimes also called a variant type^[1]) is a datatype each of whose values is data from other datatypes wrapped in one of the constructors of the datatype. Any wrapped datum is an argument to the constructor. In contrast to other datatypes, the constructor is not executed and the only way to operate on the data is to unwrap the constructor using pattern matching.

The most common algebraic data type is a list with two constructors: Nil or [] for an empty list, and Cons (an abbreviation of constructor), ::, or : for the combination of a new element with a shorter list (for example (Cons 1 '(2 3 4)) or 1:[2,3,4]).

Special cases of algebraic types are product types i.e. records (only one constructor), sum types or tagged unions (many constructors with a single argument) and enumerated types (many constructors with no arguments). Algebraic types are one kind of composite type (i.e. a type formed by combining other types).

An algebraic data type may also be an abstract data type (ADT) if it is exported from a module without its constructors. Values of such a type can only be manipulated using functions defined in the same module as the type itself.

In set theory the equivalent of an algebraic data type is a discriminated union – a set whose elements consist of a tag (equivalent to a constructor) and an object of a type corresponding to the tag (equivalent to the constructor arguments).

3. Composite data types

In computer science, composite data types are data types which can be constructed in a program using its programming language's primitive data types and other composite types. The act of constructing a composite type is known as composition.

4. Function types

Type signature is a term that is used in computer programming. A type signature defines the inputs and outputs for a function or method. A type signature includes at least the function name and the number of its parameters. In some programming languages, it may also specify the function's return type or the types of its parameters.

5. Machine data types

All data in computers based on digital electronics is represented as bits (alternatives 0 and 1) on the lowest level. The smallest addressable unit of data is a group of bits called a byte (usually an octet, which is 8 bits). The unit processed by machine code instructions is called a word (as of 2008, typically 32 or 64 bits). Most instructions interpret the word as a binary number, such that a 32-bit word can represent unsigned integer values from 0 to 2³² − 1 or signed integer values from − 2³¹ to 2³¹ − 1. Because of two's complement, the machine language and machine don't need to distinguish between these unsigned and signed data types for the most part.

There is a specific set of arithmetic instructions that use a different interpretation of the bits in word as a floating-point number.

6. Object types

In computer science, an object commonly means a data structure consisting of data fields and procedures (methods) that can manipulate those fields. Typically, when calling a method from some object, the object itself should be passed as a parameter to the method.

Objects are the foundation of object-oriented programming, and are fundamental data types in object-oriented programming languages. These languages provide extensive syntactic and semantic support for object handling, including a hierarchical type system, special notation for declaring and calling methods, and facilities for hiding selected fields from client programmers. However, objects and object-oriented programming can be implemented in any language.

Objects have proven to be very helpful in software development, particularly for large programs. For one thing, they are a natural way to implement abstract data structures, by "physically" bringing together the data components with the procedures that manipulate them. More importantly, they make it possible to handle very disparate objects by the same piece of code, as long as they all have the proper method. They also improve program reliability, simplify software maintenance, the management of libraries, and the division of work in programmer teams. Object-oriented programming languages are generally designed to exploit and enforce these potential advantages of the object model.

Outside object-oriented programming, the word object may also mean simply any entity that can be manipulated by the commands of a programming language, such as a value (computer science), variable, function, or data structure.

7. Pointer and reference data types

In computer science, a reference is a value that enables a program to directly access the particular data item, such as a variable or a record, in the computer's memory or in some other storage device. The reference is said to refer to the data item, and accessing that data is called dereferencing the reference.

A reference is distinct from the data itself. Typically, a reference is the physical address of where the data is stored in memory or in the storage device. For this reason, a reference is often called a pointer or address, and is said to point to the data. However a reference may also be the offset (difference) between the datum's address and some fixed "base" address, or an index into an array.

The concept of reference must not be confused with other values (keys or identifiers) that uniquely identify the data item, but give access to it only through a non-trivial lookup operation in some table data structure.

References are widely used in programming, especially to efficiently pass large or mutable data as arguments to procedures, or to share such data among various uses. In particular, a reference may point to a variable or record that contains references to other data. This idea is the basis of indirect addressing and of many linked data structures, such as linked lists.

A reference may be compared to a street address, such as "12 Main Street" or "three houses down the road on the left side". Going to the building with that address is analogous to dereferencing the reference. The name "Bob and Joe's Car Shop" might be a unique identifier for the same building, but cannot be compared to a data reference, because finding the building with that name requires a non-trivial search or a lookup in some directory. A reference stored in a data record can be compared to a sign on that shop saying "For tire service please go to 20 Cross Street". Passing a reference to a subroutine, instead of the data, is like giving your friend's the address of that shop, instead of taking Bob and Joe and all their tools to your friend's home.

8. Primitive data types

In computer science, primitive data type can refer to either of the following concepts:^{[citation needed]}

• a basic type is a data type provided by a programming language as a basic building block. Most languages allow more complicated composite types to be recursively constructed starting from basic types.
• a built-in type is a data type for which the programming language provides built-in support.

In most programming languages, all basic data types are built-in. In addition, many languages also provide a set of composite data types. Opinions vary as to whether a built-in type that is not basic should be considered "primitive".^{[citation needed]}

Depending on the language and its implementation, primitive data types may or may not have a one-to-one correspondence with objects in the computer's memory. However, one usually expects operations on basic primitive data types to be the fastest language constructs there are.^{[citation needed]} Integer addition, for example, can be performed as a single machine instruction, and some processors offer specific instructions to process sequences of characters with a single instruction. In particular, the C standard mentions that "a 'plain' int object has the natural size suggested by the architecture of the execution environment". This means that int is likely to be 32 bits long on a 32-bit architecture. Basic primitive types are almost always value types.

Most languages do not allow the behavior or capabilities of primitive (either built-in or basic) data types to be modified by programs. Exceptions include Smalltalk, which permits all data types to be extended within a program, adding to the operations that can be performed on them or even redefining the built-in operations.

" 3 DataBase Management System "

A database management system (DBMS) is computer software that manages databases. DBMSes may use any of a variety of database models, such as the network model or relational model. In large systems, a DBMS allows users and other software to store and retrieve data in a structured way.

A. Microsoft Office Access

-> previously known as Microsoft Access, is a relational database management system from Microsoft that combines the relational Microsoft Jet Database Engine with a graphical user interface and software development tools. It is a member of the Microsoft Office suite of applications and is included in the Professional and higher versions for Windows and also sold separately. There is no version for MacOS or for Microsoft Office Mobile.

Access stores data in its own format based on the Access Jet Database Engine. It can also import or link directly to data stored in other Access databases, Excel, SharePoint lists, text, XML, Outlook, HTML, dBase, Paradox, Lotus 1-2-3, or any ODBC-compliant data container including Microsoft SQL Server, Oracle, MySQL and PostgreSQL. Software developers and data architects can use it to develop application software and non-programmer "power users" can use it to build simple applications. It supports some object-oriented techniques but falls short of being a fully object-oriented development tool.

Microsoft Access is part of the Microsoft Office suite and is the most popular Windows desktop database application. It is targeted for the information worker market, and is the natural progression for managing data when the need for a relational database arises or after reaching the limits of Microsoft Excel.


B. Linter SQL RDBMS

->is the main product of RELEX Group. Linter is a Russian DBMS compliant with the SQL-92 standard and supporting the majority of operating systems, among them Win32 (including WinCE), NetWare, various versions of Unix, OS9, QNX, VxWorks and others. The system enables transparent interaction between the client applications and the database server functioning in different hardware and software environments. DBMS Linter includes program interfaces for the majority of popular development tools. The system provides a high data security level allowing the user to work with secret information. Linter is the only DBMS certified by FSTEC of Russia as compliant with Class 2 data security requirements and Level 2 of undeclared feature absence control. For more than ten years, Linter has been used by Russian Ministry of Defense, Ministry of Foreign Affairs and other government bodies.


C. Visual FoxPro
-> is a data-centric object-oriented and procedural programming language produced by Microsoft. It is derived from FoxPro (originally known as FoxBASE) which was developed by Fox Software beginning in 1984. Fox Technologies merged with Microsoft in 1992, after which the software acquired further features and the prefix "Visual". The last version of FoxPro (2.6) worked under Mac OS, DOS, Windows, and Unix: Visual FoxPro 3.0, the first "Visual" version, dropped the platform support to only Mac and Windows, and later versions were Windows-only. The current version of Visual FoxPro is COM-based and Microsoft has stated that they do not intend to create a Microsoft .NET version.

FoxPro originated as a member of the class of languages commonly referred to as "xBase" languages, which have syntax based on the dBase programming language. Other members of the xBase language family include Clipper and Recital. (A history of the early years of xBase can be found in the dBase entry.)

Visual FoxPro, commonly abbreviated as VFP, is tightly integrated with its own relational database engine, which extends FoxPro's xBase capabilities to support SQL query and data manipulation. Unlike most database management systems, Visual FoxPro is a full-featured, dynamic programming language that does not require the use of an additional general-purpose programming environment. It can be used to write not just traditional "fat client" applications, but also middleware and web applications.