NAME

tdom::schema - Creates a schema validation command

SYNOPSIS

package require tdom
tdom::schema ?create? cmdName


    

DESCRIPTION

Every call of this command creates a new validation command. A validation command has methods to define a schema and is able to validate XML data or to post-validate a tDOM DOM tree (and to some degree other kind of hierarchical data) against this schema.

Also, a validation command may be used as argument to the -validateCmd option of the dom parse and the expat commands to enable validation additionally to what they do otherwise.

The methods of created commands are:

prefixns ?prefixUriList?

This method controls prefix (or abbreviation) to namespace URI mapping. Wherever a namespace argument is expected in the schema command methods the "prefix" could be used instead of the namespace URI. If the list maps the same prefix to different namespace URIs, the first one wins. If there is no such prefix, the namespace argument is used literally as namespace URI. If the method is called without argument, it returns the current prefixUriList. If the method is called with the empty string, any namespace URI arguments are used literally. This is the default.

defelement name ?namespace? <definition script>

This method defines the element name (optional in the namespace namespace) in the schema. The definition script is evaluated and defines the content model of the element. If the namespace argument is given, any element or ref references in the definition script not wrapped inside a namespace command are resolved in that namespace. If there is already a element definition for the name/namespace combination, the command raises error.

defelementtype typename name ?namespace? <definition script>

This method defines the element type typename (optional in the namespace namespace) in the schema. If the element type is used in a definition script with the schema command elementtype, the validation engine expects an element named name (in the namespace namespace, if given) and the content model definition script. Defining element types seems only sensible if you really have elements with the same name and namespace but different content models. The definition script is evaluated and defines the content model of the element. If the namespace argument is given, any element or ref references in the definition script not wrapped inside a namespace command are resolved in that namespace. If there is already an elementtype definition for the name/namespace combination, the command raises error. The document element of any XML to validate cannot be a defelementtype defined element.

defpattern name ?namespace? <definition script>

This method defines a (maybe complex) content particle with the name (optional in the namespace namespace) in the schema, to be used in other definition scripts with the definition command ref. The definition script is evaluated and defines the content model of the content particle. If the namespace argument is given, any element or ref references in the definition script not wrapped inside a namespace command are resolved in that namespace. If there is already a pattern definition for the name/namespace combination, the command raises error.

deftexttype name <constraint script>

This method defines a bundle of text constraints that can be referred to by name while defining constraints on text element or attribute values. If there is already a text type definition with this name, the command raises error. A text type must be defined before it can be used in schema definition scripts.

start documentElement ?namespace?

This method defines the name and namespace of the root element of a tree to validate. If this method is used, the root element must match for validity. If start is not used, any element defined by defelement may be the root of a valid document. The start method may be used several times with varying arguments during the lifetime of a validation command. If the command is called with just the empty string (and no namespace argument), the validation constraint for the root element is removed and any defined element will be valid as root of a tree to validate.

define <definition script>

This method allows to define several elements or patterns or a whole schema with one call. All schema command methods so far (prefixns, defelement, defelementtype, defpattern, deftexttype and start) are allowed top level in the definition script. The define method itself isn't allowed recursively.

event (start|end|text) ?event specific data?

This method allows the validation of hierarchical data against the content constraints of the validation command.

validate <XML string> ?objVar?

Returns true if the <XML string> is valid, or false, otherwise. If validation has failed and the optional objVar argument is given, the variable with that name is set to a validation error message. If the XML string is valid and the optional objVar argument is given, the variable with that name is set to the empty string.

validatefile filename ?objVar?

Returns true if the content of filename is valid, or false, otherwise. The given file is feeded as binary stream to expat, therefore only US-ASCII, ISO-8859-1, UTF-8 or UTF-16 encoded data will work with this method. If validation has failed and the optional objVar argument is given, the variable with that name is set to a validation error message. If the XML string is valid and the optional objVar argument is given, the variable with that name is set to the empty string.

validatechannel channel ?objVar?

Returns true if the content read from the Tcl channel channel is valid, or false, otherwise. Since data read out of a Tcl channel is UTF-8 encoded, any misleading encoding declaration at the beginning of the data will lead to errors. If the validation fails and the optional objVar argument is given, the variable with that name is set to a validation error message. If the XML string is valid and the optional objVar argument is given, the variable with that name is set to the empty string.

domvalidate domNode ?objVar?

Returns true if the first argument is a valid tree, or false, otherwise. If validation has failed and the optional objVar argument is given, the variable with that name is set to a validation error message. If the dom tree is valid and the optional objVar argument is given, the variable with that name is set to the empty string.

reportcmd ?cmd?

This method expects the name of a Tcl command to be called in case of validation error. The command will be called with two arguments appended: the schema command which raises the validation error, and a validation error code.

delete

This method deletes the validation command.

info ?args?

This method bundles methods to query the state of and details about the schema command.

reset

This method resets the validation command into state READY (while preserving the defined grammar).

Schema definition scripts

Schema definition scripts are ordinary Tcl scripts evaluated in the namespace tdom::schema. The schema definition commands listed below in this Tcl namespace allow the definition of a wide variety of document structures. Every schema definition command establishes a validation constraint on the content which has to match or must be optional to qualify the content as valid. It is a validation error if there is additional (not matched) content. White-space-only text (in the XML sense of white space) between any different tags is ignored, with the exception of text only elements (for which even white-space-only text will be considered as significant content).

The schema definition commands are:

element name ?quant? ?<definition script>?

If the optional argument definition script is not given this command refers to the element defined with defelement with the name name in the current context namespace. If the defelement script argument is given, the validation constraint expects an element with the name name in the current namespace with content "locally" defined by the definition script. Forward references to so far not defined elements or patterns or other local definitions of the same name inside the definition script are allowed. If a forward referenced element is not defined until validation, only an empty element with name name and namespace namespace and no attributes matches.

elementtype name ?quant?

This command refers to the element defined with defelementtype with the type name name in the current context namespace. Forward references to so far not defined element types or recursive references are allowed. If a forward referenced element type is not defined until validation any empty element without attributes will be accepted.

ref name ?quant?

This command refers to the content particle defined with defpattern with the name name in the current context namespace. Forward references to a so far not defined pattern and recursive references are allowed. If a forward referenced pattern is not defined until validation no content whatsoever is expected ("empty match").

group ?quant? <definition script>

This method allows to group a sequence of content particles defined by the definition script>, which have to match in this sequence order.

choice ?quant? <definition script>

This schema constraint matches if one of the top level content particles defined by the definition script> matches. If one of this top level content particle is optional this constraint matches the "empty match".

interleave ?quant? <definition script>

This schema constraint matches after every of the required top level content particles defined by the definition script> have matched (and, optional, some or all other) in any arbitrary order.

mixed ?quant? <definition script>

This schema constraint matches for any text (including the empty one) and every top level content particle defined by the definition script> with default quantifier *.

text ?<constraint script>|“type“ typename?

Without the optional constraint script this validation constraint matches every string (including the empty one). With constraint script or with a given text type argument a text matching this script or the text type is expected.

any ?namespace? ?quant?

The any command matches every element (in the namespace namespace, if that is given) (with whatever attributes) or subtree, no matter if known within the schema or not. Please note that in case of no namespace argument is given that means that the quantifier * and + will eat up any elements until the enclosing element ends. If you really have a namespace that looks like a valid tDOM schema quantifier you will have to spell out always both arguments.

attribute name ?quant? (?<constraint script>|“type“ typename?)

The attribute command defines an attribute (in no namespace) to the enclosing element. The first definition of name inside an element definition wins; later definitions of the same name are silently ignored. After the name argument there may be one of the quantifiers ? or !. If there is, it will be used. Otherwise the attribute will be required (must be present in the XML source). If there is one argument more this argument is evaluated as constraint script, defining the value constraints of the attribute. Otherwise, if there are two more arguments and the first of them is the bare-word "type" the following argument is used as a text type name. This command is only allowed at top level in the definition script of an defelement/element script.

nsattribute name namespace ?quant? (?<constraint script>|“type“ typename?)

This command does the same as the command attribute, for the attribute name in the namespace namespace.

namespace URI <definition script>

Evaluates the definition script with context namespace URI. Every element, element type or ref command name will be looked up in the namespace URI, and local defined elements will be in that namespace. An empty string as URI means no namespace.

tcl tclcmd ?arg arg ...?

Evaluates the Tcl script tclcmd arg arg ... . This validation command is only allowed in strict sequential context (not in choice, mixed and interleave). If the return code is something else than TCL_OK, this is an error (which is not catched and reported by reportcmd).

self

Returns the schema command.

associate data

This command is only allowed top-level inside definition scripts of the element, elementtype, pattern or interleave content particles. Associates the data given as argument with the currently defined content particle and may be requested in scripts evaluated while validating the content of that particle with the schema command method call info stack associated.

domunique selector fieldlist ?name? ?“IGNORE_EMPTY_FIELD_SET“|(“EMPTY_FIELD_SET_VALUE“ emptyFieldSetValue)?

If not postvalidating a DOM tree with domvalidate this constraint always matches. If postvalidating this constraint resembles the xsd key/keyref mechanism. The selector argument may be any valid XPath expression (without the xsd limits). Several domunique commands within one element definition are allowed. They are checked in definition order. The argument name is available in the recovering script per info vaction name. If the fieldlist does not select something for a node of the result set of the selector the key value will be the empty string by default. If the arguments EMPTY_FIELD_SET_VALUE <value> are given an empty node set will have the key value value. If instead the flag IGNORE_EMPTY_FIELD_SET flag is given an empty node set result will not have any key value.

domxpathboolean XPath_expr ?name?

tdom::schema s
s define {


    defelement doc {


        element a ! text


        element b ! text


        element c ! text


        domxpathboolean "a * b * c >= 20000" volume


        domxpathboolean "a > b and b > c" sequence


    }
}


        

prefixns ?prefixUriList?

This defines a prefix to namespace URI mapping exactly as a schemacmd prefixns would. It is meant as top-level command of a schemacmd define script. This command is not allowed nested in another definition script command and will raise error, if you call it there.

defelement name ?namespace? <definition script>

This defines an element exactly as a schemacmd defelement call would. It is meant as top-level command of a schemacmd define script. This command is not allowed nested in another definition script command and will raise error, if you call it there.

defelementtype name ?namespace? <definition script>

This defines an elementtype exactly as a schemacmd defelementtype call would. It is meant as top-level command of a schemacmd define script. This command is not allowed nested in another definition script command and will raise error, if you call it there.

defpattern name ?namespace? <definition script>

This defines a named pattern exactly as a schemacmd defpattern call would. It is meant as top-level command of a schemacmd define script. This command is not allowed nested in another definition script command and will raise error, if you call it there.

deftexttype name <constraint script>

This defines a named bundle of text constraints exactly as a schemacmd deftexttype call would. It is meant as top-level command of a schemacmd define script. This command is not allowed nested in another definition script command and will raise error, if you call it there.

start name ?namespace?

This command works exactly as a schemacmd start call would. It is meant as top-level command of a schemacmd define script. This command is not allowed nested in another definition script command and will raise error, if you call it there.

Quantity specifier

Several schema definition commands expect a quantifier as one of their arguments which determines how often the content particle specified by the command is expected. The valid values for a quant argument are:

!

The content particle has to occur exactly once in valid documents.

?

The content particle may not occur more than once in valid documents - the particle is optional.

*

The content particle may occur zero or more times in a row in valid documents.

+

The content particle may occur one or more times in a row in valid documents.

n

The content particle must occur n times in a row in valid documents. The quantifier must be an integer greater zero.

{n m}

The content particle must occur at least n and at most m times in a row in valid documents. The quantifier must be a Tcl list with two elements. Both elements must be integers, with n >= 0 and n < m.

If an optional quantifier is not given, it defaults to * in case of the mixed command and to ! for all other commands.

Text constraint scripts

Text (parsed character data, as XML calls it) sometimes has to be of a certain kind or comply with certain rules to be valid. The text constraint script arguments to text, attribute, nsattribute and deftexttype commands are evaluated in the Tcl namespace tdom::schema::text namespace and allow the ensuing text constraint commands to check text for certain properties. The commands are defined in the Tcl namespace tdom::schema::text. They raise error in case they are called outside of a text constraint script.

A few of the ensuing text type commands are exposed as general Tcl commands. They are defined in the namespace tdom::type and are called as documented below with the text to check appended to the argument list. They return a logical value. Please note that the commands may not accept starting or ending white space. If a command is available in the tdom::type namespace is recorded in its documentation.

Local key constraints

Document wide uniqueness and foreign key constraints are available with the text constraint commands id and idref. Keyspaces allow for sub-tree local uniqueness and foreign key constraints.

keyspace <names list> <constraint script>

Any number of keyspaces are possible. A keyspace is either active or not. An inside a constraint script called keyspace with the same name does nothing.

This text constraint commands work with keyspaces:

key <name>

If the keyspace with the name <name> is not active the constraint always matches. If the keyspace is active, reports error if there is already a key with the value. Otherwise it stores the value as key in this keyspace and matches.

keyref <name>

If the keyspace with the name <name> is not active always matches. If the keyspace is active then reports error if there is still no key as the value at the end of the keyspace <name>. Otherwise, it matches.

Recovering

By default the validation engine stops at the first detected validation violation and reports that finding. It does so by return false (and sets, if given, the result variable with an error message) in case the schema command itself is used to validate input. If the schema command is used by a SAX parser or the DOM parser, it does so by throwing error.

If a reportcmd is set this command is called on global level appended with the schema command and an error type as arguments in case a validation violation is detected. Then the validation recovers from the error and continues. For some validation errors the recover strategy can be determined with the script result of the reportcmd.

With a reportcmd (which does not throw error if called) the validation engine will never report validation failure to its caller. The validation engine recovers, continues, and reports the next error (if occuring) and so on until the end of the input. The schema command will return true and the SAX parser and DOM builder will process normally until the end of the input, as if there had not been a validation error.

Please note that this happens only for validation errors. It is not possible to recover from well-formedness errors. If the input is not well-formed, the schema command returns false and sets (if given) the result variable with an error message about the well-formedness error.

If the reportcmd throws error while called by the validation engine then validation stops and the schema command throws error with the error message of the script.

While validating basically three events can happen: an element start tag has to match, a piece of text has to match or an element end tag has to match. The method info vaction called in the recovering script or any script code called from there returns, which event has triggered the error report (MATCH_ELEMENT_START, MATCH_TEXT, MATCH_ELEMENT_END, respectively). While the command walks throu the schema looking whether the event matches other, data driven events (as, for example checking, if any keyref within a keyspace exists) may happen.

Several of the validation error codes, appended as second argument to the reportcmd calls, may happen at more than one kind of validation event. The info vaction method and its subcommands provide information about the current validation event, if called from the report command.

If a structural validation error happens, the default recovering strategy is to ignore any following (or missing) content within the current subtree and to continue with the element end event of the subtree.

Returning "ignore" from the recovering script in case of error type MISSING_ELEMENT recovers by ignoring the failed contraint and continues to match the event further against the schema.

Returning "vanish" from the recover script in case of the error types MISSING_ELEMENT and UNEXPECTED_ELEMENT recovers by ignoring the event.

Examples

<URL: https://www.w3.org/TR/xmlschema-0/> The XML Schema Part 0: Primer Second Edition () starts with this example schema:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">


  <xsd:annotation>


    <xsd:documentation xml:lang="en">


     Purchase order schema for Example.com.


     Copyright 2000 Example.com. All rights reserved.


    </xsd:documentation>


  </xsd:annotation>


  <xsd:element name="purchaseOrder" type="PurchaseOrderType"/>


  <xsd:element name="comment" type="xsd:string"/>


  <xsd:complexType name="PurchaseOrderType">


    <xsd:sequence>


      <xsd:element name="shipTo" type="USAddress"/>


      <xsd:element name="billTo" type="USAddress"/>


      <xsd:element ref="comment" minOccurs="0"/>


      <xsd:element name="items"  type="Items"/>


    </xsd:sequence>


    <xsd:attribute name="orderDate" type="xsd:date"/>


  </xsd:complexType>


  <xsd:complexType name="USAddress">


    <xsd:sequence>


      <xsd:element name="name"   type="xsd:string"/>


      <xsd:element name="street" type="xsd:string"/>


      <xsd:element name="city"   type="xsd:string"/>


      <xsd:element name="state"  type="xsd:string"/>


      <xsd:element name="zip"    type="xsd:decimal"/>


    </xsd:sequence>


    <xsd:attribute name="country" type="xsd:NMTOKEN"


                   fixed="US"/>


  </xsd:complexType>


  <xsd:complexType name="Items">


    <xsd:sequence>


      <xsd:element name="item" minOccurs="0" maxOccurs="unbounded">


        <xsd:complexType>


          <xsd:sequence>


            <xsd:element name="productName" type="xsd:string"/>


            <xsd:element name="quantity">


              <xsd:simpleType>


                <xsd:restriction base="xsd:positiveInteger">


                  <xsd:maxExclusive value="100"/>


                </xsd:restriction>


              </xsd:simpleType>


            </xsd:element>


            <xsd:element name="USPrice"  type="xsd:decimal"/>


            <xsd:element ref="comment"   minOccurs="0"/>


            <xsd:element name="shipDate" type="xsd:date" minOccurs="0"/>


          </xsd:sequence>


          <xsd:attribute name="partNum" type="SKU" use="required"/>


        </xsd:complexType>


      </xsd:element>


    </xsd:sequence>


  </xsd:complexType>


  <!-- Stock Keeping Unit, a code for identifying products -->


  <xsd:simpleType name="SKU">


    <xsd:restriction base="xsd:string">


      <xsd:pattern value="\d{3}-[A-Z]{2}"/>


    </xsd:restriction>


  </xsd:simpleType>
</xsd:schema>


    

A likely one-to-one translation of that into a tDOM schema definition script would be:

tdom::schema schema      
schema define {


    # Purchase order schema for Example.com.


    # Copyright 2000 Example.com. All rights reserved.


    defelement purchaseOrder {ref PurchaseOrderType}


    foreach elm {comment name street city state product} {


        defelement $elm text


    }


    defpattern PurchaseOrderType {


        element shipTo ! {ref USAddress}


        element billTo ! {ref USAddress}


        element comment ?


        element items


        attribute orderDate date


    }


    defpattern USAddress {


        element name


        element street


        element city


        element state


        element zip ! {text number}


        attribute country ! {fixed "US"}


    }


    defelement items {


        element item * {


            element product


            element quantity ! {text integer}


            element USPrice ! {text number}


            element comment


            element shipDate ? {text date}


            attribute partNum ! {pattern "^\d{3}-[A-Z]{2}$"}


        }


    }
}


      


    

<URL: http://relaxng.org/tutorial-20011203.html> The RELAX NG Tutorial () starts with this example:

Consider a simple XML representation of an email address book:
<addressBook>


  <card>


    <name>John Smith</name>


    <email>js@example.com</email>


  </card>


  <card>


    <name>Fred Bloggs</name>


    <email>fb@example.net</email>


  </card>
</addressBook>
The DTD would be as follows:
<!DOCTYPE addressBook [
<!ELEMENT addressBook (card*)>
<!ELEMENT card (name, email)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT email (#PCDATA)>
]>
A RELAX NG pattern for this could be written as follows:
<element name="addressBook" xmlns="http://relaxng.org/ns/structure/1.0">


  <zeroOrMore>


    <element name="card">


      <element name="name">


        <text/>


      </element>


      <element name="email">


        <text/>


      </element>


    </element>


  </zeroOrMore>
</element>


      


    

This schema definition script will do the same:

tdom::schema schema      
schema define {


    defelement addressBook {


        element card *


    }


    defelement card {


        element name


        element email


    }


    foreach e {name email} {


        defelement $e text


    }
}


      


    

KEYWORDS

Validation, Postvalidation, DOM, SAX