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Incomputer programming,orthogonality means that operations change just one thing without affecting others.[1] The term is most-frequently used regarding assembly instruction sets, asorthogonal instruction set.
Orthogonality in a programming language means that a relatively small set of primitive constructs can be combined in a relatively small number of ways to build the control and data structures of the language.[2] It is associated with simplicity; the more orthogonal the design, the fewer exceptions. This makes it easier to learn, read and write programs in a programming language.[citation needed] The meaning of an orthogonal feature is independent of context; the key parameters are symmetry and consistency (for example, a pointer is an orthogonal concept).
An example from IBM Mainframe and VAX highlights this concept. An IBM mainframe has two different instructions for adding the contents of aregister to a memory cell (or another register). These statements are shown below:
A Reg1, memory_cellAR Reg1, Reg2
In the first case, the contents ofReg1 are added to the contents of a memory cell; the result is stored inReg1. In the second case, the contents ofReg1 are added to the contents of another register (Reg2) and the result is stored inReg1.
In contrast to the above set of statements, VAX has only one statement for addition:
ADDL operand1, operand2
In this case the two operands (operand1 andoperand2) can be registers, memory cells, or a combination of both; the instruction adds the contents ofoperand1 to the contents ofoperand2, storing the result inoperand1.
VAX's instruction for addition is more orthogonal than the instructions provided by IBM; hence, it is easier for the programmer to remember (and use) the one provided by VAX.
TheRevised Report on the Algorithmic Language Algol 68 had this to say about "Orthogonal design":
The number of independent primitive concepts has been minimized in order that the language be easy to describe, to learn, and to implement. On the other hand, these concepts have been applied "orthogonally" in order to maximize the expressive power of the language while trying to avoid deleterious superfluities.
The design of C language may be examined from the perspective of orthogonality. The C language is somewhat inconsistent in its treatment of concepts and language structure, making it difficult for the user to learn (and use) the language. Examples of exceptions follow:
Though this concept was first applied to programming languages, orthogonality has since become recognized as a valuable feature in the design of APIs and even user interfaces. There, too, having a small set of composable primitive operations without surprising cross-linkages is valuable, as it leads to systems that are easier to explain and less frustrating to use.
On the other hand, orthogonality does not necessarily result in simpler systems, as the example ofIBM andVAX instructions shows — in the end, the less orthogonalRISC CPU architectures were more successful than theCISC architectures.
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