OML - AbsoluteAstronomy.com

OML can also be the abbreviation for Open Modeling Language, Old Main Line
Old Main Line
The Old Main Line can refer to*BCN Old Main Line, a canal network in Birmingham, England*BMT Lexington Avenue Line*Old Main Line Subdivision of CSX Transportation...

, Oregon Medical Laboratories, One More Level or Old Mutual
Old Mutual
Old Mutual plc is an international long-term savings group. Established in 1845 in South Africa, it is now a FTSE100 listed company operating in 33 countries.-History:...

.

OML (Outline Markup Language) is an XML

XML

Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....

format for outline

Outline

An outline is a list of the main features of a given topic, often used as a rough draft or summary of the content of a document. A hierarchical outline is a list arranged to show hierarchical relationships, and is a type of tree structure....

s. It was originally proposed by Ray Grieselhuber. The specification is designed to build upon the concepts found in OPML

OPML

OPML is an XML format for outlines...

, with the goal of fixing some of its limitations.

OML has a structure similar to OPML. Its advocates claim that although it is as simple and as flexible as OPML, its extension mechanism is better than that of OPML. Instead of letting users add attributes freely, OML introduces an element (child element of ); instances of the element may be added freely.

The resulting documents are claimed to be easier to parse than equivalent OPML documents. Readers of OPML never know what attributes others may have added to standard elements; so an element the reader wants to parse may contain a mixture of known and unknown attributes. This claimed disadvantage of OPML actually applies to any XML

XML

-based format, including OML, because XML namespace

XML Namespace

xmlns tagged XML namespaces are used for providing uniquely named elements and attributes in an XML document. They are defined in a W3C recommendation. An XML instance may contain element or attribute names from more than one XML vocabulary...

s may add attributes to existing tags; however, OPML is unusual in its enthusiasm for free-form definition of new attributes. In OML, extensions are added in the form of s instead; an unknown may be discarded without harming known data elsewhere in the file. The approach taken by OML is designed to be more in keeping with the approach of other XML-based languages and with the philosophy of some standards organizations.

Despite its claimed advantages, OML has not seen wide use. Reasons for the greater popularity of OPML may include the relative newness of OML (finalized in May 2003), and non-technical political issues between members of the XML

XML

community.

Critics of OML point out OML doesn't have a mechanism to preserve whitespace. Some have also found the distinction between and unnecessary.

See also