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In computer science, a record (also called struct or compound data)〔Felleisen et al., ''How To Design Programs'', MIT Press, 2001〕 is a basic data structure. A record is a collection of ''elements'', possibly of different data types, typically in fixed number and sequence. The elements of records may also be called ''fields'' or ''members''. A tuple may or may not be considered a record, and vice versa, depending on conventions and the specific programming language. For example, a date could be stored as a record containing a numeric year field, a month field represented as a string, and a numeric day-of-month field. A Personnel record might contain a name, a salary, and a rank. A Circle record might contain a center and a radius—in this instance, the center itself might be represented as a point record containing x and y coordinates. Records are distinguished from arrays by the fact that their number of fields is typically fixed, each field has a name, and that each field may have a different type. A ''record type'' is a data type that describes such values and variables. Most modern computer languages allow the programmer to define new record types. The definition includes specifying the data type of each field and an identifier (name or label) by which it can be accessed. In type theory, product types (with no field names) are generally preferred due to their simplicity, but proper record types are studied in languages such as System F-sub. Since type-theoretical records may contain first-class function-typed fields in addition to data, they can express many features of object-oriented programming. Records can exist in any storage medium, including main memory and mass storage devices such as magnetic tapes or hard disks. Records are a fundamental component of most data structures, especially linked data structures. Many computer files are organized as arrays of logical records, often grouped into larger physical records or blocks for efficiency. The parameters of a function or procedure can often be viewed as the fields of a record variable; and the arguments passed to that function can be viewed as a record value that gets assigned to that variable at the time of the call. Also, in the call stack that is often used to implement procedure calls, each entry is an ''activation record'' or ''call frame'', containing the procedure parameters and local variables, the return address, and other internal fields. An object in object-oriented language is essentially a record that contains procedures specialized to handle that record; and object types are an elaboration of record types. Indeed, in most object-oriented languages, records are just special cases of objects, and are known as plain old data structures (PODSs), to contrast with objects that use OO features. A record can be viewed as the computer analog of a mathematical tuple. In the same vein, a record type can be viewed as the computer language analog of the Cartesian product of two or more mathematical sets, or the implementation of an abstract product type in a specific language. ==Keys== A record may have zero or more ''key''s. A key is a field or set of fields in the record that serves as an identifier. A unique key is often called the ''primary key'', or simply the ''record key''. For example an employee file might contain employee number, name, department, and salary. The employee number will be unique in the organization and would be the primary key. Depending on the storage medium and file organization the employee number might be ''indexed''—that is also stored in a separate file to make lookup faster. The department code may not be unique; it may also be indexed, in which case it would be considered a ''secondary key'', or ''alternate key''. If it not indexed the entire employee file would have to be scanned to produce a listing of all employees in a specific department. The salary field would not normally be considered usable as a key. Indexing is one factor considered when designing a file. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Record (computer science)」の詳細全文を読む スポンサード リンク
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