Introduction
This document describes how to produce a customization of the TEI P5 schema. From the start, the TEI was intended to be used as a set of building blocks for creating a schema suitable for a particular project. This is in keeping with the TEI philosophy of providing a vocabulary for describing texts, not dictating precisely what those texts must contain or might have contained. This means that it is likely, not just possible, that you will want to have a tailored view of the TEI.
What do we mean by a ‘customization’? It is important to understand that there is no single DTD or schema which is the TEI; you always choose from the available modules (there are currently 23 of them, listed in the module list below) those that you want, with the caveat that the modules core, header, textstructure, and tei, when using RELAX NG) should always be chosen unless you are certain you know what you are doing. Components from these modules are referred to throughout the other modules, and hence these modules cannot be eliminated without careful adjustments.
Although there is no default schema, TEI P5 does provide a number of example customizations which may very well meet your needs; these can be downloaded from the TEI web site or from within the Roma interface:
- tei_bare: TEI Absolutely Bare
- teilite: TEI Lite
- tei_corpus: TEI for Linguistic Corpora
- tei_ms: TEI for Manuscript Description
- tei_drama: TEI with Drama
- tei_speech: TEI for Speech Representation
- tei_odds: TEI for authoring ODD
- tei_allPlus: TEI with maximal setup, plus external additions
- tei_svg: TEI with SVG
- tei_math: TEI with MathML
- tei_xinclude: TEI with XInclude
Choosing the basic set of modules may be sufficient, but it’s also possible that you may want to tailor your TEI schema more tightly. For instance, once you have decided that your application will make use of the msdescription and linking modules, you may also want to
- remove elements from some of the modules which you do not expect to use, to reduce confusion and avoid the accidental use of elements you don’t need
- rename elements
- add, delete or change attributes for existing elements, perhaps to make the datatype stricter
- add new elements, and insert them into the TEI class system
We will be seeing examples of each of these in the following sections.
Below is a table of all of the TEI modules. More information about each one is given in the TEI Guidelines; each module corresponds to a single chapter.
The TEI modules
| module name | title | elements defined |
| analysis | Simple analytic mechanisms | 11 |
| certainty | Certainty and uncertainty | 3 |
| core | Elements common to all TEI documents | 83 |
| corpus | Header extensions for corpus texts | 14 |
| dictionaries | Dictionaries and other lexical resources | 33 |
| drama | Performance texts | 17 |
| figures | Tables, formulae, and figures | 7 |
| gaiji | Character and glyph documentation | 14 |
| header | The TEI Header | 72 |
| iso-fs | Feature structures and feature system | 28 |
| linking | Linking, segmentation and alignment | 12 |
| msdescription | Manuscript Description | 69 |
| namesdates | Names and dates | 56 |
| nets | Graphs, networks and trees | 12 |
| spoken | Transcribed Speech | 14 |
| tagdocs | Documentation of TEI modules | 54 |
| tei | Declarations for datatypes, classes, and macros available to all TEI modules | 0 |
| textcrit | Text criticism | 14 |
| textstructure | Default text structure | 33 |
| transcr | Transcription of primary sources | 30 |
| verse | Verse structures | 4 |
Writing ODD specifications
‘ODD’ (One Document
Does it All
) is a TEI XML format used to express schema fragments, prose documentation, and reference
documentation for any XML markup scheme as a single document. It is the language in which the TEI is itself defined,
and which should also be used to express a customization of the TEI scheme.
The concepts
of ODD were devised and implemented by Lou Burnard and Michael Sperberg-McQueen early in
the development of the TEI. The language developed over time as the TEI was put
together, and one form of it was documented in the TEI Guidelines (versions 3 and 4);
unfortunately, that version of the markup was not what was actually used to write the
TEI Guidelines, which diverged into a more complex scheme. For version 5 of the TEI, the
entire ODD language was revised and simplified by a working group led by
Sebastian Rahtz, and the Guidelines themselves brought into conformance with it.
An ODD specification is a normal TEI XML document which includes components from the
tagdocs module. This module is fully described in
the TEI Guidelines chapter Documentation Elements. The Guidelines also describe in some detail
how an ODD file should be processed: see chapter Using the TEI. The current document is a tutorial introduction to the information more fully presented in the Guidelines.
The recommended way to customize the TEI is to create a formal specification expressing your customizations, as an XML document using TEI ODD markup; this can then be compiled into a suitable DTD, RELAX NG schema or W3C Schema (together with the appropriate reference documentation), using the Roma program. Roma is a web-based interface for creating TEI customizations, which allows you to fill in simple forms to choose modules, add and delete elements, change attributes, and make other customizations. More advanced users can also create or edit an ODD by hand using normal XML editing tools.
There are several important reasons why this high-level method is recommended:
- Ihe resulting specification can be used to generate a schema in any currently popular schema language (DTD, RELAX NG schema, W3C schema).
- The specification is expressed using the familiar TEI markup.
- The specification is complete in itself and can be transferred to other TEI-aware applications or users without worrying about any dependencies
Key concepts
There are several core components in the TEI infrastructure which you should understand before creating or editing your own ODD files. The concept of modules has been explained above: TEI elements and attributes are organized into a set of modules which group them according to their purpose.
Elements are normally defined in the context of modules. For example, the castList element is defined in the drama module. An element is defined (or ‘declared’) using the <elementSpec> element.
In addition to being defined in modules, elements are also organized into model
classes. A model class is a method of grouping a number of elements together so
that they can be referred to easily as a group. For example,
model.graphicLike
‘groups elements containing images, formulae, and similar objects’, such as
<formula> and <graphic>. Other elements (for instance <figure>)
can then make use of this model as part of their content definition. Model classes are
defined using the <classSpec> element, with the attribute
type="model". The <classSpec> does not contain a list of elements
which belong to the class; instead, elements “claim membership” of the class through
<memberOf> elements in their own <elementSpec>s.
Attributes are always defined using the <attDef> element, but they
may be defined in two different contexts. Some attributes are defined directly on
elements; in other words, their definition forms part of the definition of the element
on which they appear. For example, the age
element, which is used to specify the age of a person, has an attribute called
@value, which holds the numeric value of the person’s age. This attribute is
defined directly as part of the definition of the <age> element itself.
Other attributes are used on a range of different elements. It is not efficient or
practical to define the same attribute multiple times, once on each element, so these
attributes are defined as part of attribute classes. The Guidelines
provides a list of all the TEI attribute classes. Each class provides one or more
attributes which are likely to be useful in a particular context or for a particular
purpose. For example, the @source attribute, which is used to provide a
pointer to a bibliographical source for a quotation or reference, is defined in the
att.source class. The elements <quote>, <q>,
<writing> and <egXML> each declare membership of the
att.source class, and thus acquire the @source attribute.
Attribute classes may be nested. In other words, one attribute class may be a member of
another. This is a convenient way of grouping similar classes of attributes so that an
element can claim membership of all of them in one operation. For example, there are
three base attribute classes relating to dating attributes:
att.datable.iso (providing attribute for expression of dates in ISO
format), att.database.w3c (providing attributes for dates in W3C format),
and att.datable.custom (for dates in non-Gregorian calendars). There is
also the att.datable class, of which the other three are all members. An
element which claims membership of att.datable (such as <date>)
will acquire all the attributes in the three base classes. Attribute classes are defined
using the classSpec element, with the attribute
type="atts".
The final important concept is the idea of a macro. A macro is basically a method of re-using the same block of content in multiple places. The most common macros are those which define datatypes for TEI attributes. For example, the data.count macro provides the definition of a positive integer, which is used as the datatype for more than 20 different attributes. Defining this datatype in one location avoids duplication and provides consistency. Other macros are used to define content models which are useful in the definition of many different elements; for instance, the macro.paraContent macro ‘defines the content of paragraphs and similar elements’, and is used in the definition of 50 different elements. Macros are defined using the <macroSpec> element.
With this basic introduction to how elements, attributes and their components and relationships are defined, you may now want to take a look at some example specifications from the TEI repository:
- The <age> element contains one attribute definition, as mentioned
above; it is also a member of three attribute classes, and one model class. If you
look at the root <elementSpec> element, you’ll see the attribute
module="namesdates"; this is what determines that this element is part of the namesdates (Names and Dates) module. - The
att.typed attribute class defines two attributes,
@typeand@subtype. It is part of the tei module. - The model.orgPart specification demonstrates how simple a model class specification can be.
The basic structure of a <gi><schemaSpec>
A TEI schema is defined by a <schemaSpec> element containing an arbitrary mixture of explicit declarations for objects (i.e. elements, classes, or macro specifications) and references to other objects containing such declarations. In simplified form, the data model is
where <elementSpec>, <macroSpec> and <classSpec> contain definitions of TEI objects. <moduleRef> references groups of existing definitions, in one of two ways:
- If the key attribute is provided, it refers to the TEI name for a module, and details of that are accessed from the TEI web service database (which may be a local installation).
- If the url attribute is provided, it refers to an external file of schema definitions in the RELAX NG language (this is used to pull in non-TEI schemas)
In the simplest case, a user-defined schema might simply combine all the declarations from some nominated modules:
Note that this is a normal TEI document, with a TEI header to supply some metadata. In the other examples that follow, we will usually omit the outer TEI wrapper and just show the <schemaSpec> element.
An ODD processor, given such a document, will combine the declarations which belong to the named modules, and deliver the result as a schema of some requested type. It might also generate documentation for all (and only) the elements declared by those modules. The start attribute of <schemaSpec> is used to specify which elements are valid entry points in a RELAX NG schema .
You can address individual elements or classes by adding <elementSpec>, <classSpec> or <macroSpec> elements after <moduleRef>. Each of these must have a mode attribute on it, which can take four values:
- add
- the object is entirely new.
- replace
- the object entirely replaces the existing object with the same ident.
- delete
- all references to the original object with the same ident are removed from the schema.
- change
- child elements of the object which appear in the original specification are replaced by the versions in the new specification. This may be at any level, as we will see in examples below.
It is an error to provide replace, delete or
change versions for objects which do not already exist in the TEI, and an
error to add something with the same ident attribute as an existing
object in the TEI.
Adding new elements
A schema can include declarations for new elements, as in the following example:
A declaration for the element <soundClip>, which is not defined in the TEI scheme, will be added to the output schema. This element will also be added to the existing TEI class model.pPart.data, and will thus be avilable in TEI conformant documents.
In the following example we add a new element <rebirth> which is modelled on the existing <birth> element:
There are usually four parts to such an element definition:
- An identifier (in this case the value
rebirthfor the ident attribute). - Documentation (the <gloss> and <desc> elements)
- Declaration of which classes this element is to be a member of (att.datable and att.naming); this is the same as <birth>, which we have to find out by looking at the definition of that
- The content model for the element, here the general purpose pattern macro.phraseSeq
There is no need to specify a module for the element to appear in, as this would not be used for anything.
Removing elements
Specifing that we do not want some of the elements to appear in our final schema is easy:
Note that no child elements of the deleted object are needed, or taken notice of.
Changing existing elements
When we come to changing existing elements, the specification looks a little more complex:
In this example, we are changing the behaviour of the
<div> element so that the type attribute (inherited from the
class att.divLike) is mandatory and chosen from a fixed set of values.
The change value for mode must be supplied on each
identifiable part of the object which is to change. So the <elementSpec> itself
is in change mode, plus the <attDef> for type, while
the <valList> is in replace mode. The elements we have
not specified any change for (examples, references, etc) are copied from
the original.
Change mode can apply to classes as well as elements. In the following example, we remove a set of attributes which are provided for any element which is a member of the att.linking class:
If you want to change which elements belong to add.linking, you must change the <classes> element of each of the elements separately.
Adding new elements in in a different namespace
A good example of this would be if you wanted to use the W3C XInclude scheme in your XML. This is a way of referring to external files to be transcluded (DTD users will be familiar with the use of file entities to perform this job). This document, for example, pulls in a table (created by an automatic process) by using this piece of code:
Since the <include> could occur anywhere, we want to add it to a TEI class which is referenced almost everywhere; model.inter does this job nicely. We could pull in an external schema which defines <include>, but it may be amusing to define it ourselves using this <elementSpec>:
Note the new ns attribute on <elementSpec> which says that this element is not to be defined in the default (TEI) namespace.
Processing your ODD specification
When you have finished writing your customization, you can turn your ODD into schemas or DTDs for use with XML editors or validators, or create schema documentation showing the specification for your elements and classes.
There are a few options for carrying out both of these tasks:
Roma (command line)
An ODD specification can be processed in a scripting environment by using the roma command-line script. This takes the form:
By default the script creates DTD, XSD and RELAX NG schemas, each of these can be suppressed if needed, and a set of summary documentation can be created. The xsl and teiserver options point to resources which roma needs to do its job; if you have a local copy of the TEI XSL stylesheets, or a local TEI eXist database, you can make the script independent of web access.
For information on using the web-based interface to roma, see Creating Customizations with Roma.
Making use of non-TEI schemas
The TEI was designed to capture all the vagaries of literary and linguistic text; it does not attempt to describe other specialised descriptive languages, such as those for chemistry, mathematics, and vector graphics, or the technical vocabulary of fields like law, health care and computer science. Some of the areas have been addressed as thoroughly as the TEI in their own standards. But what if we want to write a composite document mixing material from two fields? Since all the TEI elements are in their own XML namespace, it is easy to write a document which interleaves TEI markup with markup from another namespace, as in this example of TEI and Docbook:
But what about validating this XML against a schema? Using the Namespace-based Validation Dispatching Language (see), we can validate the two languages separately, but we also want a TEI customization which checks where insert of ‘foreign’ elements is permitted. This means importing another schema, and changing one or more TEI classes to allow for the new element(s). If it is also required that TEI elements be allowed inside the elements of the other namespace, we also have to modify the other namespace.
Two common cases which do not require interleaving are:
- redefining the content of <formula> to allow for MathML markup.
- redefining the content of <figure> to allow SVG markup.
In each case, we first need a <moduleRef> which loads the external schema in RELAX NG format:
These schemas can be downloaded
from MathML and SVG; note that they may each need a small fix to remove the RELAX NG <start>
pattern, as this causes a conflict with the TEI definition. These define respectively two
patterns called mathml.math and svg.svg, which we can proceed to add
to TEI content models.
- For MathML, we redefine the content of the TEI <formula> element:
<schemaSpec ident=”tei_math” prefix=”tei_” start=”TEI teiCorpus” xmlns:teix=”http://www.tei-c.org/ns/Examples” defaultExceptions=”http://www.w3.org/1998/Math/MathML http://www.tei-c.org/ns/1.0 teix:egXML”> <moduleRef url=”https://www.tei-c.org/release/xml/tei/Exemplars/mathml2-main.rng”/> <moduleRef key=”header”/> <moduleRef key=”core”/> <moduleRef key=”tei”/> <moduleRef key=”textstructure”/> <moduleRef key=”figures”/> <elementSpec module=”figures” ident=”formula” mode=”change”> <content> <elementRef key=”mathml.math”/> </content> </elementSpec> </schemaSpec>
- For SVG, we need to change the model of <figure>, simply adding a reference
to
svg.svgat the end of a <choice> list:<elementSpec ident=”figure” mode=”change” xml:base=”examples/addsvg.xml”> <content> <rng:zeroOrMore xmlns:rng=”http://relaxng.org/ns/structure/1.0″> <rng:choice> <rng:ref name=”model.Incl”/> <rng:ref name=”figure”/> <rng:ref name=”figDesc”/> <rng:ref name=”graphic”/> <rng:ref name=”head”/> <rng:ref name=”p”/> <rng:ref name=”svg.svg”/> </rng:choice> </rng:zeroOrMore> </content> </elementSpec>