Ad hoc computer network

In philosophy and science, ad hoc often means the addition of corollary hypotheses or adjustment to a philosophical or scientific theory to save the theory from being falsified by compensating for anomalies not anticipated by the theory in its unmodified form. Philosophers and scientists are often suspicious or skeptical of theories that rely on continual, inelegant adjustments, and ad hoc hypotheses are often a characteristic of pseudoscientific subjects. See Skeptic's Dictionary: Ad hoc hypothesis. Much of scientific understanding relies on the modification of existing hypotheses or theories, but these are distinguished from ad hoc hypotheses in that the anomalies being explained propose a new means of being falsified.
Theories that have been empirically tested and rather than being confirmed they seem either to have been falsified or to require numerous ad hoc hypotheses to sustain them include applied kinesiology, astrology, biorhythms, facilitated communication, plant perception, and ESP.[1] Despite evidence contrary to the theories, adherents do not give them up. For example, ESP researchers have been known to blame the hostile thoughts of onlookers for unconsciously influencing pointer readings on sensitive instruments.
An interesting example of an ad hoc hypothesis is Albert Einstein's addition of the cosmological constant to relativity in order to allow a steady-state universe. Although he later referred to it as his greatest mistake, it has been found to correspond quite well to the theories of dark energy.
Many reference works employ ad hoc pronunciation schemas as a way of indicating how words are pronounced. These are especially popular in U.S. published works[citation needed], such as the Merriam-Webster dictionary. An example of an ad hoc pronunciation would be "DIK-shuh-nair-ee", where the capitalization shows which syllable is stressed. This is in contrast to systems such as the International Phonetic Alphabet, which attempt to put pronunciation schemas on a scientific footing.
Critics of ad hoc schemes point out that such schemas are inherently self-referential, since they rely on the ability of the reader to already know how a large number of words are commonly pronounced. In addition, such schemas often assume a certain language, dialect or accent on the part of the reader, and due to its popularity in the US, this is very often a US accent.
As its name suggests, there is no "standard" ad hoc schema, and so examples will vary considerably according to the publication's whim. In contrast, the IPA seeks to base pronunciation solely on vocal tract configurations and on the phonemes produced, though very often neo-common simple words are used to illustrate how the IPA applies in a specific language.
Proponents of ad hoc claim that it is much easier to use than IPA, though will often concur that this is usually only because the pronunciation is already known.
Many application software systems have an underlying database which can be accessed by only a limited number of queries and reports. Typically these are available via some sort of menu, and will have been carefully designed, pre-programmed and optimized for performance by expert programmers.
By contrast, "ad hoc" reporting systems allow the users themselves to create specific, customised queries. Typically this would be via a user-friendly GUI-based system without the need for the in-depth knowledge of SQL, or database schema that a programmer would have.
Because such reporting has the potential to severely degrade the performance of a live system, it is sometimes provided only on a regularly-refreshed copy of the "live" database. Depending on the context, such a copy might be referred to as a data warehouse and the querying as data mining.

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