How To Make New Tag Sets
Parameter Entities Modules to Customize and Change
Parameter entities are the major mechanism for customizing this Tag Set or creating a new tag set from the modules in the Suite. Individual tag sets will be constructed by (1) establishing element and attribute combinations and content models using parameter entities in one of the Tag-Set-specific customizing modules and (2) choosing appropriate modules from the Suite that declare the elements needed. For example, if a base tag set contained 6 kinds of lists and 2 table models, a more specific tag set, such as an authoring tag set, might use a Customize Classes Module to redefine the List Class to name only 3 lists and redefine the Display Class to allow only one table model.
The standard modules to create a customized tag set are: the DTD itself, a module to name its components, and as many override modules and new elements modules as necessary. Typical modules for a new tag set are:
- DTD — The DTD module (.dtd) for the new tag set base DTD (At a minimum, this module declares the top-level element (such as book or book part wrapper) and any other structural elements unique to the new document type.)
- Tag-Set-specific Module of Modules — Module to name all the new modules created expressly for the new Tag Set
- Class overrides — Tag-Set-specific overrides of the Suite default element classes
- Mix overrides — Tag-Set-specific overrides of the Suite default class mixes
- Model overrides — Tag-Set-specific content model overrides for the content models in the modules of the Suite (using “-elements” and “-model” parameter entities)
- New Models — Tag-Set-specific new elements (For example, a new legislative Book Tag Set might add legislation-specific metadata elements.)
Element Classes Concept
Many of the elements in the BITS Book Tag Set have been grouped into loose element classes. There is no hard and fast rule for what constitutes a class; each one is a design decision, a matter of judgment. These classes are designed to ease customization to meet the particular needs of new tag sets. Base classes for the NISO JATS DTD Suite are defined in a separate Default Element Classes Module (%default-classes.ent;).
Content models are built using sequences of elements, and OR groups that are classes (typically) or mixes. As an example, the content model for a Paragraph element is declared to be an OR group (that is, a choice) of data characters and any of the elements named in the Paragraph Elements mix. The mix %p-elements; is declared to be a large OR group of many other element-defining classes: the Block Display Class Elements, the Mathematical Expressions Class Elements, the List Class Elements, the Citation Class Elements, etc.
Implementor’s Note: These element classes can be viewed as building blocks that will be used to build larger parameter entities for element mixes. A mix describes a usage circumstance for a group of elements, such as all the paragraph-level elements, all the elements allowed inside a table cell, all the elements inside a paragraph, or all the inline elements. For example, to add another block display item to the Block Display Class Elements, you would edit the %block-display.class; parameter entity (and probably also the Display Class No Alternatives Elements parameter entity) in your Tag-Set-specific Class Override Module to override the default parameter entity defined in the Suite’s Default Element Classes Module and create a new module containing the Element Declaration of the new block display item.
Parameter Entity Names for Classes and Mixes
PARAMETER ENTITY: SAME FUNCTION, SAME NAME — The Suite modules and initial Tag Sets have used a series of parameter entity naming conventions consistently. While parsing software cannot enforce these parameter entity naming or usage conventions, these conventions can make it much easier for a person to know how the content models work and what must be modified to make a Tag Set change.
CLASSES — Classes are functional groupings of elements used together in an OR group. Each class is named with a parameter entity, and all class parameter entity names end in the suffix “.class”:
<!ENTITY % list.class "def-list | list">
A class, by definition, should never be made empty; the class should be removed from all models where you do not want the class elements included.
MIXES — Mixes are functional OR groups of classes; mixes should never contain element names directly. All mixes must be declared after all classes, since mixes are composed of classes. Mix names have no set suffix; for example, they may end in “-mix” or “-elements”. Content models and content model overrides use mixes and classes for all OR groups. Only content model sequences are made up of element names directly.
MODEL OVERRIDES — Parameter entity mixes for overriding a content model are of two styles: (1) inline mixes and (2) full content model replacements. These two groupings have been defined and named separately to preserve the mixed-content or element-content nature of the models in Tag Sets derived from the Suite.
The inline parameter entities to be intermingled with character data (#PCDATA) in a mixed content model are named with a suffix “-elements”. For example, “%institution-elements;” would be used in the content model for the element <institution>:
<!ENTITY % institution-elements "| %all-phrase; | %break.class;" > <!ELEMENT institution (#PCDATA %institution-elements;)* >
All inline mixes begin with an OR bar, so that the mix can be removed leaving just character data (#PCDATA):
<!ENTITY % rendition-plus "| %all-phrase;" >
The override of a complete content model will be named with a suffix “-model” and should include the entire content model, including the enclosing parentheses:
<!ENTITY % kwd-group-model "(label?, title?, ((%kwd.class; | %x.class;)+ | %unstructured-kwd-group.class;))" > <!ELEMENT kwd-group %kwd-group-model; >
How To Build a New Custom Tag Set
The basic idea for a new Tag Set is that all lower-level elements (paragraphs, lists, figures, etc. and as much of the metadata as possible) will be defined in modules — either the modules of the base Suite or in new Tag-Set-specific modules rather than in the DTD itself. The new DTD will be fairly short and include only definitions of the topmost elements, at least the document element and maybe its children.
Modules are declared using external parameter entities in the Suite’s Module to Name the JATS Modules or in the Tag-Set-specific Module of Modules. Modules are referenced in the DTD proper, in the order needed to define the parameter entities in sequence.
This BITS Book Tag Set was written as an example of the new best-practice customization technique. A new variant tag set that follows this plan will probably consist of the following modules:
- A DTD module to define the top-level elements (for example, BITS-book2.dtd);
- A Tag-Set-specific Module of Modules to name new non-Suite modules in this Tag Set (for example, BITS-bookcustom-modules2.ent);
- A Tag-Set-specific definition of element classes to add new classes and override the default classes (for example, BITS-bookcustom-classes2.ent);
- A Tag-Set-specific definition of element mixes to add new mixes and override the default mixes (for example, BITS-bookcustom-mixes2.ent);
- A Tag-Set-specific module of content model overrides (for example, BITS-bookcustom-models2.ent);
- Tag-Set-specific modules to hold new element declarations; and
- All or most of the modules in the Suite.
Making a Variant Tag Set
To show the process, here is a series of instructions for making a new tag set, illustrated by showing how the BITS Book Tag Set was created from the modules of the whole Suite.
- Modules — Write a new Tag-Set-specific Module of Modules, which defines all new customization modules the tag set needs. As an example, the BITS Book Tag Set created the module BITS-bookcustom-modules2.ent, which contains the definitions of the class-override module BITS-bookcustom-classes2.ent, the mix-override module BITS-bookcustom-mixes2.ent, the models-override module BITS-bookcustom-models2.ent, and the BITS specific modules such as BITS-book-part2.ent.
- Class overrides — Write a Tag-Set-specific class-override module, defining any overrides to the Suite classes. These classes are defined in the default classes module, JATS-default-classes1.ent. As an example, the BITS Book Tag Set created the module BITS-bookcustom-classes2.ent, in which %date.class; and %rest-of-para.class; were redefined.
- Mix overrides — Write a Tag-Set-specific mix-override module, defining any overrides to the Suite mixes. These mixes are defined in the default mixes module, JATS-default-mixes1.ent. As an example, the BITS Book Tag Set created the module BITS-bookcustom-mixes2.ent, in which mix overrides such as %emphasized-text; and %sec-back-matter-mix; were declared.
- Model overrides — Create a Tag-Set-specific content-model-override module, defining any overrides to the content models and attribute lists for the Suite. As an example, the BITS Book Tag Set created the module BITS-bookcustom-models2.ent, in which element collections (suffixed “-elements”) that will be mixed with #PCDATA were redefined, full content models overrides (suffixed “-model”) were redefined, and some new attributes and attribute lists were added.
- New Elements — Write any new element modules needed. These will define any new block-level or phrase-level elements. For the BITS Book Tag Set, there were several such modules, for book-specific metadata, to define the models for book parts, and for structural indexes and Tables of Contents.
- DTD Module — With those modules in place,
construct a new DTD module. Within that module:
- Use an external parameter entity Declaration to name and then call the Tag-Set-specific module of modules, for the BITS Book Tag Set, the module BITS-bookcustom-modules2.ent.
- Use an external parameter entity Declaration to name and then call the Suite Module of Modules, which names all the potential modules, for the full JATS, the module JATS-modules1.ent.
- Use an external parameter entity reference to call the Tag-Set-specific class overrides, for the BITS Book Tag Set, the module BITS-bookcustom-classes2.ent.
- Use an external parameter entity reference to call the Suite default classes, for the BITS Book Tag Set, the module JATS-default-classes1.ent.
- Use an external parameter entity reference to call the Tag-Set-specific mix overrides, for the BITS Book Tag Set, the module BITS-bookcustom-mixes2.ent.
- Use an external parameter entity reference to call the Suite default mixes, for the BITS Book Tag Set, the module JATS-default-mixes1.ent.
- Use an external parameter entity reference to call the Tag-Set-specific content models and attribute list overrides, for the BITS Book Tag Set, the module BITS-bookcustom-models2.ent.
- Use an external parameter entity reference to call in the standard Common Module (JATS-common2.ent) that defines elements and attributes so common they are used by many modules.
- Use an external parameter entity reference to call any new Tag-Set-specific module defining new block-level or phrase-level elements. For the BITS Book Tag Set, there are many such modules, for example, the book-specific metadata.
- Select, from the Module of Modules, those modules which contain the elements needed for your Tag Set (for instance, selecting lists and not selecting math elements) and call in each of the modules needed. The BITS Book Tag Set calls these in alphabetical order, since the order does not matter.
- Define the document element and any other unique elements and entities needed for this Tag Set. For example, the BITS Book Tag Set declares only a few elements including: <book> [the top-level element] and its potential components: <book-meta>, <front-matter>, <body>, and <back>.