Encoded Archival Description Tag Library, Version 2002
EAD Attributes: Introduction
Attributes are associated with most of the elements contained in EAD. These attributes reflect named properties of an element and may take on different values, depending on the context in which they occur. In order to set one or more attributes, an encoder should include the name of the attribute(s) within the same angle bracket as the start tag, together with the value(s) to which the attribute(s) is/are to be set. That is,
<[tag] [attribute1]="[value1]" [attribute2]="[value2]">
<origination label="Creator:">Kenny, Elizabeth</origination>
Most attributes are optional and of the type called #IMPLIED. Two attributes are flagged as #REQUIRED, that is, the LEVEL attribute on <archdesc> and <archdescgrp>, and the COLS attribute on <tgroup>, and two are #FIXED.
#IMPLIED-- The attribute is not required. If no attribute value is specified, a processing program may infer a value.
#REQUIRED-- The attribute must be specified within the start tag for the element, e.g.:
#FIXED-- The attribute has only one possible value which is specified by the DTD.
The value of attributes may be constrained by the DTD using specific attribute type values. For example, "id" attribute is of type ID, which constrains its value to a string beginning with an alphabetic character. An "id" value must be unique within the EAD instance within which it occurs, that is, no other tag in the entire document can have the same "id" value. Most EAD attributes are of type CDATA, which means that any text characters may be used.
CDATA: -- Character data. No markup is recognized within a CDATA value except for character references. If the characters < (less than), > (greater than), & (ampersand), ' (apostrophe), or " (quotation) are used, they must be escaped using a character reference.
ENTITY: -- The name of a nonparsed entity that has been declared in the declaration subset of the document. For example, the ENTITYREF attribute must contain the name of an entity that has been declared in the declaration subset. Processing software can use the reference to the nonparsed entity to display the entity in the body of the text or in a new window.
ID: -- Unique identifier. For example, most elements have an ID attribute,
so that a unique code can be established for and used to refer to that specific
element. The content of the ID attribute is of the type called "id." Parsers
verify that the value of attributes of type "id" are unique. ID attribute values
must begin with an alpha, not numeric, character, either upper or lowercase,
and may contain a . (period),
IDREF: -- ID reference value; previously entered ID of another element. For example, the <container> element has a PARENT attribute that can only be an "idref," which means it has a reference to a valid ID in another element.
IDREFS: -- List of ID reference values.
NMTOKEN: -- A name token, which can consist of any alpha or numeric character, as well as a . (period), : (colon), - (hyphen), or _ (underscore), but not a blank space. A number of attributes in EAD where a character string from a code list is to be used are NMTOKEN.
NMTOKENS: -- List of name tokens.
When the EAD DTD limits attribute values to a few choices, those values are declared in the DTD as part of what is known as a closed list, or technically, a name-token list. For example, the values of the attribute AUDIENCE are limited to either "external" or "internal." Some attributes are associated with semi-closed lists. Such lists include those values believed to be the most useful in many contexts. Since the DTD creators could not anticipate all useful values for an attribute of this type, the list permits, by means of another attribute, the ability to provide an alternative value. For example, the <dsc> element includes several display types in a semi-closed list. Setting the TYPE attribute to "othertype" makes it possible to specify in a separate OTHERTYPE attribute display types that are not in the semi-closed list for TYPE. The definitions for some values in the closed and semi-closed lists appear below.
The following is a complete list of all the attributes that occur in EAD, and some discussion of how they may be used. Attributes that are used for linking and for tabular display are defined in separate lists that follow the General Attributes list.
May 25, 2006