Ad hoc

Ad hoc is a Latin phrase which means "for this [purpose]." It generally signifies a solution that has been tailored to a specific purpose and is makeshift and non-general, such as a tailor-made suit, a handcrafted network protocol or a specific-purpose equation, as opposed to general solutions. It can also refer to an improvised and often impromptu event or solution "on an ad-hoc basis", as opposed to well-prepared ones. It comes from the Latin phrase meaning 'to the thing'.

Ad hoc computer network

In computer networking, ad hoc is a network connection method which is most often associated with wireless devices. The connection is established for the duration of one session and requires no base station. Instead, devices discover others within range to form a network for those computers. Devices may search for target nodes that are out of range by flooding the network with broadcasts that are forwarded by each node. Connections are possible over multiple nodes (multihop ad hoc network). Routing protocols then provide stable connections even if nodes are moving around. Both Nintendo's DS and Sony's PlayStation Portable use ad hoc connections for wireless multiplayer gaming.

See IEEE 802.11, Bluetooth, or ultra-wide band. The alternative is infrastructure, with a base station that manages the network for its range.

The term ad hoc network can also refer to an independent basic service set (IBSS).

Ad hoc committee

Ad hoc is also used to describe a particular type of committee; one which is formed to deal with a particular issue, and disbanded after the issue is resolved. These committees provide stop gap or temporary measures to solve problems that are not resolved by ordinary processes of the organization to which the committee belongs. The GATT], for example, was controlled by an ad-hoc committee before the WTO was established.

Ad hoc hypothesis

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 ad hoc 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.

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.

Ad hoc pronunciation

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, 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 schemas 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 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.

Ad hoc querying

Ad hoc querying is a term in information science.

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.

External Links

A review of several ad-hoc reporting tools