XML Glossary

A

archiving

Saving the state of an object and restoring it.

 

attribute

A qualifier on an XML tag that provides additional information. For example, in the tag <slide title="My Slide">, title is an attribute, and My Slide is its value.

B

binary entity

See unparsed entity.

binding

Construction of the code needed to process a well-defined bit of XML data.

C

comment

Text in an XML document that is ignored, unless the parser is specifically told to recognize it. A comment is enclosed in a comment tag, like this: <!-- This is a comment -->

 

content

The part of an XML document that occurs after the prolog, including the root element and everything it contains.

 

CDATA

A predefined XML tag for "Character DATA" that says "don't interpret these characters", as opposed to "Parsed Character Data" (PCDATA), in which the normal rules of XML syntax apply (for example, angle brackets demarcate XML tags, tags define XML elements, etc.). CDATA sections are typically used to show examples of XML syntax. Like this:

    <![CDATA[ <slide>..A sample slide..</slide> ]]>

which displays as:

   <slide>..A sample slide.. </slide> 

D

 

data

The contents of an element, generally used when the element does not contain any subelements. When it does, the more general term content is generally used. When the only text in an XML structure is contained in simple elements, and elements that have subelements have little or no data mixed in, then that structure is often thought of as XML "data", as opposed to an XML document.

 

DDP

Document-Driven Programming. The use of XML to define applications.

 

declaration

The very first thing in an XML document, which declares it as XML. The minimal declaration is <?xml version="1.0"?>. The declaration is part of the document prolog.

 

document

In general, an XML structure in which one or more elements contains text intermixed with subelements. See also: data.

 

DOM

Document Object Model. A tree of objects with interfaces for traversing the tree and writing an XML version of it, as defined by the W3C specification.

 

DTD

Document Type Definition. An optional part of the document prolog, as specified by the XML standard. The DTD specifies constraints on the valid tags and tag sequences that can be in the document. The DTD has a number of shortcomings however, which has led to various schema proposals. For example, the DTD entry <!ELEMENT username (#PCDATA)> says that the XML element called username contains "Parsed Character DATA" -- that is, text alone, with no other structural elements under it. The DTD includes both the local subset, defined in the current file, and the external subset, which consists of the definitions contained in external .dtd files that are referenced in the local subset using a parameter entity.

E

element

A unit of XML data, delimited by tags. An XML element can enclose other elements. For example, in the XML structure, "<slideshow><slide>..</slide><slide>..</slide></slideshow>", the <slideshow> element contains two <slide> elements.

entity

A distinct, individual item that can be included in an XML document by referencing it. Such an entity reference can name an entity as small as a character (for example, "<", which references the less-than symbol, or left-angle bracket (<). An entity reference can also reference an entire document, or external entity, or a collection of DTD definitions (a parameter entity).

entity reference

A reference to an entity that is substituted for the reference when the XML document is parsed. It may reference a predefined entity like < or it may reference one that is defined in the DTD. In the XML data, the reference could be to an entity that is defined in the local subset of the DTD or to an external XML file (an external entity). The DTD can also carve out a segment of DTD specifications and give it a name so that it can be reused (included) at multiple points in the DTD by defining a parameter entity.

error

A SAX parsing error is generally a validation error -- in other words, it occurs when an XML document is not valid, although it can also occur if the declaration specifies an XML version that the parser cannot handle. See also: fatal error, warning.

external entity

An entity that exists as an external XML file, which is included in the XML document using an entity reference.

external subset

That part of the DTD that is defined by references to external .dtd files.

F

fatal error

A fatal error occurs in the SAX parser when a document is not well formed, or otherwise cannot be processed. See also: error, warning.

G

general entity

An entity that is referenced as part of an XML document's content, as distinct from a parameter entity, which is referenced in the DTD. A general entity can be a parsed entity or an unparsed entity

H

HTML

HyperText Markup Language. The language of the Web. A system where every document has a globally unique location, and documents can link to one another.

L

local subset

That part of the DTD that is defined within the current XML file.

M

mixed-content model

A DTD specification that defines an element as containing a mixture of text and one more other elements. The specification must start with #PCDATA, followed by alternate elements, and must end with the "zero-or-more" asterisk symbol (*). For example:

       <!ELEMENT item (#PCDATA | item)* 

N

namespace

A standard that lets you specify a unique label to the set of element names defined by a DTD. A document using that DTD can be included in any other document without having a conflict between element names. The elements defined in your DTD are then uniquely identified so that, for example, the parser can tell when an element called <name> should be interpreted according to your DTD, rather than using the definition for an element called "name" in a different DTD.

normalization

The process of removing redundancy by modularizing, as with subroutines, and of removing superfluous differences by reducing them to a common denominator. For example, line endings from different systems are normalized by reducing them to a single NL, and multiple whitespace characters are normalized to one space.

 

notation

A mechanism for defining a data format for a non-XML document referenced as an unparsed entity. This is a holdover from SGML that creaks a bit. The newer standard is to use MIME datatypes and namespaces to prevent naming conflicts.

O

OASIS

Organization for the Advancement of Structured Information Standards. Their home site is http://www.oasis-open.org/. The DTD repository they sponsor is at http://www.XML.org.

P

parameter entity

An entity that consists of DTD specifications, as distinct from a
general entity. A parameter entity defined in the DTD can then be referenced at other points, in order to prevent having to recode the definition at each location it is used.

 

parsed entity

A general entity which contains XML, and which is therefore parsed when inserted into the XML document, as opposed to an unparsed entity.

 

parser

A module that reads in XML data from an input source and breaks it up into chunks so that your program knows when it is working with a tag, an attribute, or element data. A nonvalidating parser ensures that the XML data is well formed, but does not verify that it is valid.
See also: validating parser.

 

processing instruction

Information contained in an XML structure that is intended to be interpreted by a specific application.

 

prolog

The part of an XML document that precedes the XML data. The prolog includes the declaration and an optional DTD.

R

reference

See entity reference

RDF

Resource Description Framework. A standard for defining the kind of data that an XML file contains. Such information could help ensure semantic integrity, for example by helping to make sure that a date is treated as a date, rather than simply as text.

RDF schema

A standard for specifying consistency rules (for example, price must be greater than zero, discount must be less than 15%) that apply to the specifications contained in an RDF.

root

The outermost element in an XML document. The element that contains all other elements.

S

SAX

"Simple API for XML". An event-driven interface in which the parser invokes one of several methods supplied by the caller when a "parsing event" occurs. "Events" include recognizing an XML tag, finding an error, encountering a reference to an external entity, or processing a DTD specification.

schema

A database-inspired method for specifying constraints on XML documents using an XML-based language. Schemas address deficiencies in DTDs, such as the inability to put constraints on the kinds of data that can occur in a particular field (for example, all numeric). Since schemas are founded on XML, they are hierarchical, so it is easier to create an unambiguous specification, and possible to determine the scope over which a comment is meant to apply.

SGML

Standard Generalized Markup Language. The parent of both HTML and XML. However, while HTML shares SGML's propensity for embedding presentation information in the markup, XML is a standard that allows information content to be totally separated from the mechanisms for rendering/displaying that content.

T

tag

A piece of text that describes a unit of data, or element, in XML. The tag is distinguishable as markup, as opposed to data, because it is surrounded by angle brackets (< and >). For example, the element <name>My Name</name> has the start tag <name>, the end tag </name>, which enclose the data "My Name". To treat such markup syntax as data, you use an entity reference or a CDATA section.

U

Unicode

A standard defined by the Unicode Consortium that uses a 16-bit "code page" which maps digits to characters in languages around the world. Because 16 bits covers 32,768 codes, Unicode is large enough to include all the world's languages, with the exception of ideographic languages that have a different character for every concept, like Chinese. For more info, see http://www.unicode.org/.

unparsed entity

A general entity that contains something other than XML. By its nature, then, an unparsed entity contains binary data.

URI

A "Universal Resource Identifier". A URI is either a URL or a URN. (URLs and URNs are concrete entities that actually exist. A "URI" is an abstract superclass -- it's a name we can use when we know we are dealing with either an URL or an URN, and we don't care which.

URL

Universal Resource Locator. A pointer to a specific location (address) on the Web that is unique in all the world. The first part of the URL defines the type of address. For example, http:/ identifies a Web location. The ftp:/ prefix identifies a downloadable file. Other prefixes include file:/ (a file on the local disk system) and mailto:/ (an email address).

URN

Universal Resource Name. A unique identifier that identifies an entity, but doesn't tell where it is located. That lets the system look it up to see if a local copy exists before going out to find it on the Web. It also allows the web location to change, while still allowing the object to be found.

V

valid

A valid XML document, in addition to being well formed, conforms to all the constraints imposed by a DTD. In other words, it does not contain any tags that are not permitted by the DTD, and the order of the tags conforms to the DTD's specifications.

 
validating parser

A validating parser is a parser which ensures that an XML document is valid, as well as well-formed.
See also: parser.

W

w3c

The World Wide Web Consortium. The international body that governs Internet standards.

warning

A SAX parser warning is generated when the document's DTD contains duplicate definitions, and similar situations that are not necessarily an error, but which the document author might like to know about, since they could be. See also: fatal error, error.

well-formed

A well-formed XML document is syntactically correct. It does not have any angle brackets that are not part of tags. (The entity references < and > are used to embed angle brackets in an XML document.) In addition, all tags have an ending tag or are themselves self-ending (<slide>..</slide> or <slide/>). In addition, in a well-formed document, all tags are fully nested. They never overlap, so this arrangement would produce an error: <slide><image>..</slide></image>. Knowing that a document is well formed makes it possible to process it. A well-formed document may not be valid however. To determine that, you need a validating parser and a DTD.

X

XHTML

An XML lookalike for HTML defined by one of several XHTML DTDs. To use XHTML for everything would of course defeat the purpose of XML, since the idea of XML is to identify information content, not just tell how to display it. XHTML makes the conversion from HTML to XML, though. You can also reference it in a DTD, which allows you to say, for example, that the text in an element can contain <em> and <b> tags, rather than being limited to plain text.

XLink

The part of the XLL specification that is concerned with specifying links between documents.

XLL

The XML Link Language specification, consisting of XLink and XPointer.

XML

Extensible Markup Language, which allows you to define the tags (markup) that you need to identify the data and text in XML documents.

 

XML Schema

The w3c schema specification for XML documents..

XPath

See XSL.

 

XPointer

The part of the XLL specification that is concerned with identifying sections of documents so that they can referenced in links or included in other documents.

 

XSL

Extensible Stylesheet Language. An important standard that achieves several goals. XSL lets you:

1. Specify an addressing mechanism, so you can identify the parts of an XML file that a transformation applies to. (XPath)
2. Specify tag conversions, so you convert XML data into a different formats. (XSLT)
3. Specify display characteristics, such page sizes, margins, and font heights and widths, as well as the flow objects on each page. Information fills in one area of a page and then automatically flows to the next object when that area fills up. That allows you to wrap text around pictures, for example, or to continue a newsletter article on a different page. (XML-FO)

 

XSL-FO

Extensible Stylesheet Language Formatting Objects. See XSL.

 

XSLT

Extensible Stylesheet Language Transformations. See XSL.

XML Glossary

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