Expert: Chuck Cosby - 4/16/2009

Question
Hi
could you plz tell me about the function of 'implies' in boolean ADT(abstract data type)
i should write the ADT for implies but i dont know what it is doing

Thanx
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Answer
my expertize is in Natural Language and i don't use boolean anymore.  I never heard of 'implies' - Just And, Or, Xor, Nor, Nand, etc.  However, i did a search on the Internet.  Here is what i found:



An ADT (Abstract Data Type) is a mathematical formalism for defining the characteristics of a certain data type, without revealing the underlying model, let alone any concrete implementation in a computer program. An ADT defines exactly what is required of an implementation, and, by omission, also what is not required.

Marshalling is the process of linearizing a data structure into a sequence of bytes in a certain, previously agreed-upon way, so that one process can pass its internal data structure to another process, which will then be able to build an equivalent data structure. Since the marshalling algorithm presented here is based on the ADT, and not on an actual model, or even implementation, the two processes are free to use different internal memory structures. As a consequence, the marshalled data contains exactly enough information that a round-trip is possible, but no more.

XML is a very rich data type that contains Strings and Identifiers, partly ordered in a sequence, partly hierarchical, partly in an unordered database-like keyword/value system.

Fundamental functions
The functions defined here together define the ADT XML. The ADT makes use of previously defined types Identifier, URL, char, int, boolean, and nil, as well as of powersets and sequences of these. For example, the set consisting of all possible sequences of chars is denoted as char[] and the collection consisting of all possible sets of Identifiers is denoted as 2Identifier. The empty set is written as {}.

ADT XMLNode

import Identifier, URL, char, int, boolean, nil

The functions and the invariants that define them are as follows (`x' is the Cartesian product; `A -> B' means the function is from A to B; `=>' stands for `implies'; `+' is the set union operator for sets, and the normal addition operator for ints; `<>' means `not equal'; `\' is set difference):