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The schema in
Languages. The lang-check abstract rule checks that the element being checked contains exactly as many translation children as there are languages defined in the languages element. This rule can then be reused for any element that provides information in two languages. A separate rule with context="translation" additionally checks that the lang attributes correspond to the defined languages and that each language version is provided only once.
Element presence.
In this schema, many element-presence checks are lumped together
for simplicity (e.g., all children of an environment are
checked in one assert). This does not have to be that
way; if you want your schema to be really helpful, you can write a
separate check with its own diagnostic message for each element type, explaining its
role and the possible consequences of its being missing from
Context-sensitive checks. Note that there are two different page element types: One is used in the master document, and the other is the root element type in a page document. The same applies to blocks. The schema, however, has no problems differentiating between these element types based on the context.
Reporting unknowns.
One function of a schema is to check for unknown element type
names (most often resulting from typos). In Schematron, this can be
implemented by providing a dummy rule with no tests,
listing all defined element types as possible contexts. Following
that, a rule with context="*" signals error whenever
the rule is activated. This technique is possible because each
context will only match one rule per pattern; if an element was not
matched by the dummy rule, it is caught by the next rule and
reported as
It’s only a beginning.This example schema demonstrates only the basic, most critical
checks. Your own schema may be significantly larger and more
detailed than this, although it will likely use mostly the same
techniques. Consider this schema a phrasebook with common
expressions for typical situations. Several advanced tricks for
validating complex constraints are discussed in
<schema xmlns="http://www.ascc.net/xml/schematron"> <!-- Checks for the master document: --> <pattern name="master"> <rule context="site"> <report test="count(//environment) = 1"> Only one 'environment' found; you will need to create more if you want to build the site in a different environment. </report> <report test="count(//environment) = 0"> No 'environment' elements found; the stylesheet will be unable to figure out pathnames. </report> <assert test="languages and menu and html-title and page-footer and blocks"> One of the required elements not found inside 'site'. </assert> </rule> <rule context="page-footer"> <assert test="copyright and language-switch and contact-webmaster"> One of the required elements not found inside 'page-footer'. </assert> </rule> <rule context="environment"> <assert test="src-path and out-path and target-path and img-path and os"> One of the required elements not found inside 'environment'. </assert> <assert test="@id"> An 'environment' must have an 'id' attribute. </assert> <assert test="count(//environment/@id[. = current()/@id]) = 1"> The 'id' attribute value of an 'environment' must be unique. </assert> </rule>
<rule context="src-path | img-path | out-path | target-path"> <report test="*"> The '<name/>' element cannot have children. </report> <report test="(normalize-space(.) = '') and not(name() = 'target-path')"> The '<name/>' element cannot be empty. </report> </rule> <rule context="languages"> <assert test="count(lang) = count (*)"> The 'languages' element can only have 'lang' children. </assert> <assert test="count(lang) > 0"> The 'languages' element must have at least one 'lang' child. </assert> </rule> <rule context="languages/lang"> <assert test="count(//languages/lang[. = current()]) = 1"> Each language must be specified only once. </assert> </rule> <rule context="menu"> <assert test="count(item) = count (*)"> The 'menu' element cannot contain elements other than 'item'. </assert> </rule> <rule context="item"> <assert test="label" diagnostics="label-element"> A 'label' element is missing. </assert> <report test="count(label) > 1" diagnostics="label-element"> There is an extra 'label' element. </report> <assert test="page"> At least one 'page' element should be specified within an 'item'. </assert> </rule>
<rule context="menu//page"> <assert test="@src"> Each 'page' must have an 'src' attribute. </assert> <assert test="@id"> Each 'page' must have a unique 'id' attribute. </assert> <assert test="count(//page/@id[. = current()/@id]) = 1"> The 'id' attribute value of a 'page' must be unique. </assert> </rule> <!-- Abstract rule to check 'transformation' children: --> <rule abstract="true" id="lang-check"> <assert test="count(translation) = count(//languages/lang)"> The number of 'translation' children in '<name/>' must correspond to the number of defined languages. If this element does not exist in one of the languages, use an empty 'translation' element. </assert> <assert test="count(translation) = count(*)"> There must be no child elements here other than 'translation'. </assert> </rule> <!-- Applying the abstract rule to all bilingual elements: --> <rule context="label | html-title | copyright | language-switch | contact-webmaster | button"> <extends rule="lang-check"/> </rule> <rule context="translation"> <assert test="@lang"> Each 'translation' must have a 'lang' attribute. </assert> <assert test="@lang = //languages/lang/text()"> The value of the 'lang' attribute must correspond to one of the defined languages. </assert> <report test="@lang = preceding-sibling::translation/@lang"> There is another 'translation' element under this parent with the same value of the 'lang' attribute. </report> </rule>
<rule context="blocks"> <report test="*[not(self::block or self::block-process)]"> A 'blocks' element must only contain one or more 'block' or 'block-process' elements. </report> </rule> <rule context="blocks/block"> <assert test="@id and @src"> A 'block' defined in the master document must have both 'id' and 'src' attributes. </assert> <assert test="count(//blocks/block/@id[. = current()/@id]) = 1"> The 'id' attribute value of a 'block' must be unique. </assert> </rule> </pattern> <!-- Checks for page documents: --> <pattern name="page"> <rule context="/page"> <assert test="@keywords"> Please consider adding a list of keywords to the page. Use a 'keywords' attribute for that. </assert> <assert test="title"> Each 'page' must have a 'title'. </assert> <assert test="count(title) < 2"> A 'page' may have only one 'title'. </assert> <assert test="block"> Each 'page' must have at least one 'block'. </assert> </rule> <rule context="page//block"> <assert test="@idref or *"> A block must have either an 'idref' attribute (referring to an orthogonal block) or children. </assert>
<report test="@idref and *"> A block cannot have both an 'idref' attribute and children. </report> <report test="count(p | section) < count(*)"> A block can only have 'p' or 'section' children. </report> </rule> <rule context="section"> <assert test="head"> A section must have a 'head'. </assert> <assert test="p"> A section must have at least one 'p' (paragraph). </assert> <assert test="normalize-space(text()) = ''"> A section cannot contain text. Use a 'p' element to include a paragraph of text. </assert> </rule> </pattern> <!-- Rules common for master and page documents: --> <pattern name="common"> <rule context="int | link[@linktype='internal']"> <assert test="@link"> An internal link must use a 'link' attribute to specify the page being linked. </assert> </rule> <rule context="p"> <report test="(normalize-space(text()) = '') and not(*)"> A paragraph cannot be empty. If you want to increase vertical spacing here, modify the stylesheet. </report> </rule>
<!-- Dummy rule listing all defined element types: --> <rule context=" block | block-process | blocks | button | buttons | contact-webmaster | copyright | environment | em | ext | head | html-title | img-path | int | item | label | lang | language-switch | languages | link | mailto | menu | os | out-path | p | page | page-footer | site | section | src-path | subhead | target-path | title | translation"/> <!-- Report error if an element was not matched by the above: --> <rule context="*"> <report test="true()"> Unrecognized element: '<name/>'. </report> </rule> </pattern> <diagnostics> <diagnostic id="label-element"> Every 'item' element must contain exactly one 'label' element specifying the corresponding top menu label. </diagnostic> </diagnostics> </schema>
1. www.w3.org/TR/2003/WD-xhtml2-20030131/
2. Formatting attributes such as font, color, or numbering style are out of the question — the whole point of semantic XML is that these must be abstracted away.
3. A linked element is often called an anchor, and HTML uses this term for both the source of the link (source anchor) and its destination (destination anchor); hence the use of the a element for both ends of a link.
4. In Western writing systems, of course.
5. www.oasis-open.org/specs/docbook.shtml
8. www.nitf.org
10. An RFC (Request for Comments) is one of the series of standards created by the Internet Engineering Task Force (IETF) and governing most of the underlying technical structure of the Internet.
11. Strictly speaking, HTML links to URIs, not pathnames, but links within a site almost always use relative or absolute pathnames (without a server part) that are also valid URIs.
12. Unfortunately, this only works for your own site. Visitors coming from another site linking to yours will still get a 404 for a moved page.
13. www.w3.org/TR/xhtml-modularization/abstract_modules.html#s_forms
15. It might be argued that the size of an input field is one of its essential semantic aspects and not a superficial formatting property.
16. www.exslt.org/dyn/functions/evaluate
17. The single slash character in this URL means that the file is available locally and not on a network host.
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Created: March 27, 2003
Revised: May 24, 2004
URL: http://webreference.com/programming/xsltweb2/1
