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a proposition that expresses permission or a requirement to perform or refrain from performing, under particular conditions, some act; the word “act” is understood to refer to some action or absence of action. These rules are called rules of permission and obligation, respectively; they are considered in a natural way to be elementary, or rules of the first rank, and are subsumed under the general term “injunction.” Complex rules are rules of the (n+ 1)th rank, obtained by applying injunctions to collections of rules of the nth or lesser rank in such a way that at least one of these rules must be of the nth rank. Ordinary grammatical rules are examples of rules of different, but not very high, ranks. A method is a system of rules of different ranks that includes rules designating the order in which other rules of the same system are introduced and rearranged.
Rules, whose systematic study is the object of deontic (normative) logic, are of importance in daily life and in all branches of science, particularly mathematics, logic, linguistics, ethics, jurisprudence, sociology, and political economy.
algorithmA set of ordered steps for solving a problem, such as a mathematical formula or the instructions in a program. The terms algorithm and "program logic" are synonymous as both refer to a sequence of steps to solve a problem. However, an algorithm often implies a more complex problem rather than the input-process-output logic of typical business software. See encryption algorithm.
filter(1) See packet filter and filter bubble.
(2) To select data. Filters use patterns (masks) against which data are compared and only matching data are "passed through," hence the concept of a filter. For example, email clients and servers can look for messages with text patterns that are recognized as spam (see spam filter and Bayesian filtering). An email filter can also be configured to send messages into specific mailboxes or forward mail to another address based on any matching criteria in the message. See algorithmic filter.
(3) To change data. For example, a sort routine changes the sequence of data. A conversion routine (import or export filter) changes one type of data, text or graphics format into another. See import filter, image filter and parse.