The Web Ontology Language – Making A Universally Parsable Data Format
The Web Ontology Language (or OWL) is a W3C Recommended Practice for packaging and presenting data in ways that are useful to computers, and is one of the fundamental ground layers of the development of the World Wide Web into an extension called the Semantic Web, where every piece of data that's transmitted contains the meta-data needed to parse it, and to define how it interrelates with other data types.
The ultimate aim of OWL is to provide a framework for that information, so that classes, dependencies and resources can be defined clearly in a universally accepted format.
The closest physical analogy to OWL is IKEA furniture, which is all made to standardized parts and assembly instructions.
OWL provides the specifications for the size of the box, (the data structure), the standard location of where the packing list, and the fact that it's written in English, rather than carved on a clay tablet, (the definition of the data types in the box), along with the assembly instructions (how those data types interact with each other), plus the list of tools needed (what data manipulation constructs are needed to use the data) and how they interact.
Where OWL differs from XML (Extensible Markup Language) and RDF (Resource Definition Formation) is that XML is a data type that might be in the box (for example: "Shelf:Pine, 30" wide by 9" deep") while RDF is a tool definition ("Allen Key, 5 mm diameter. Fits into 5 mm Allen Key Socket"). OWL provides a way of packaging those data elements and tools into one box, while making sure that that box can be understood by anyone who's familiar with the formatting.
As its name implies, OWL is an ontological construct. OWL doesn't specify what the data is; it defines what kinds of data are allowed in a given data structure (or box). Going back to the IKEA box analogy, if the OWL statement does not include chainsaws or unicorns, it's reasonable to assume that there is no RDF for the class of manipulators known as chainsaws in the box, nor are there any XML schemas for four legged ungulates with a single horn.
OWL comes in three forms: OWL Lite, OWL DL and OWL Full. The simplies way to describe the difference is that they provide different (and greater vocabularies) of terms that can be used to describe data as you go up the progression from Lite to Full. Any definition or term specified in OWL Lite will be valid in OWL DL and OWL Full; however it's possible to define terms in OWL Full that would not work in OWL Lite.
This three layer approach means that users who don't want to spend a lot of time attempting to define everything can work within the constraints of OWL Lite, while those who need to have extreme levels of customization of the definition of what can be contained in a data structure may want to delve into OWL Full, which will result in significantly more complicated end documents.
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