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XML support

There are three levels of support for XML with EST.

- Loading as an Utterance: A built in XML parser allows text marked up according to an XML DTD to be read into an EST_Utterance (see Reading XML Text As An EST_Utterance).
- XML_Parser_Class: A C++ class XML_Parser_Class which makes it relatively simple to write specialised XML processing code.
- RXP: The RXP XML parser is included and can be used directly (The RXP XML Parser).

# Reading XML Text As An EST_Utterance

In order to read XML marked up text, the EST code must be told how the XML markup should relate to the utterance structure. This is done by annotating the DTD using which the text is processed.

There are two possible ways to anotate the DTD. Either a new DTD can be created with the anotations added, or the anotations can be included in the XML file.

A new DTD

To write a new DTD based on an existing one, you should include the existing one as follows:

<!-- Extended FooBar DTD for speech tools -->
<!-- Include original FooBar DTD -->
<!ENTITY % OldFooBarDTD PUBLIC "//Foo//DTD Bar"
"http://www.foo.org/dtds/org.dtd">
%OldFooBarDTD;
<!-- Your extensions, for instance... -->
<!-- syn-node elements are nodes in the Syntax relation -->
<!ATTLIST syn-node relationNode CDATA #FIXED "Syntax" >

In the XML file

Extensions to the DTD can be included in the !DOCTYPE declaration in the marked up text. For instance:

<?xml version='1.0'?>
<!DOCTYPE utterance PUBLIC "//Foo//DTD Bar"
"http://www.foo.org/dtds/org.dtd"
[
<!-- Item elements are nodes in the Syntax relation -->
<!ATTLIST item relationNode CDATA #FIXED "Syntax" >
]>
<utterance>
<!-- Actual markup starts here -->

## Summary of DTD Anotations

The following attributes may be added to elements in your DTD to describe it's relation to EST_Utterance structures.

- estUttFeats: The value should be a comma separated list of attributes which should be set as features on the utterance. Each attribute can be either a simple identifier, or two identifiers separated by a colon :.

  A value foo:bar causes the value of the foo attribute of the element to be set as the value of the Utterance feature bar.

  A simple identifier foo causes the foo attribute of the element to be set as the value of the Utterance feature X_foo where X is the name of the element.

- estRelationFeat: The value should be a comma separated list of attributes which should be set as features on the relation related to this element. It's format and meaning is the same as for estUttFeats.
- estRelationElementAttr: Indicates that this element defines a relation. All elements inside this one will be made nodes in the relation, unless they are explicitly marked to be ignored by estRelationIgnore. The value of the estRelationElementAttr attribute is the name of an attribute which gives the name of the relation.
- estRelationTypeAttr: When an element has a estRelationElementAttr tag to indicate it's content defines a relaion, it may also have the estRelationTypeAttr tag. This gives the name of an attribute which gives the type of relation. Currently only a type of list' or linear' gives a lienar relation, anything else gives a tree.
- estRelationIgnore: If this is set to any value on an element which would otherwise be interpreted as an EST_Item in the current relation, the element is passed over. The contents will be processed as if they had been directly inside this element's parent.
- estRelationNode: When placed on an element, indicates that this element is to be interpreted as an item in the relation named in the value of the attribute.
- estExpansion: The value of this attribute defines how ranges in href attributes are expanded for this element. If the value is replace the nodes created during expansion are placed at the same level in the hierachy as the original element. If the value is embed they are created as children of a new node.
- estContentFeature: The value of this attribute is the featre which is set to the contents of the current element.

# The XML_Parser_Class C++ Class

The C++ class XML_Parser_Class (declared in rxp/XML_Parser.h) defines an abstract interface to the XML parsing process. By breating a sub-class of XML_Parser_Class you can create code to read XML marked up text quite simply.

## Some Definitions

- An XML parser is an object which can analyse a piece of text marked up according to an XML doctype and perform actions based on the markup. One XML parser deals with one text.
- An XML parser is represented by an instance of the class XML_Parser.
- An XML parser class is an object from which XML parses can be created. It defines the behaviour of the parsers when they process their assigned text, and also a mapping from XML entity IDs to places to look for them.
- An XML parser class is represented by an instance of XML_Parser_Class or a subclass of XML_Parser_Class.

## Creating An XML Processing Procedure

In order to create a procedure which will process XML marked up text in the manner of your choice you need to do 4 things. Simple examples can be found in testsuite/xml_example.cc and main/xml_parser_main.cc.

### Create a Sub-Class of XML_Parser_Class

Not written

### Create a Structure Holding the State of the Parse

Not written

### Decide How Entity IDs Should Be Converted To Filenames

Not written

### Write A Procedure To Start The Parser

Not written

## The XML_Parser_Class in Detail

Not written

- XMLParser

# The RXP XML Parser

Included in the EST library is a version of the RXP XML parser. This version is limited to 8-bit characters for consistency with the rest of EST. For more details, see the RXP documentation.

Insert reference to RXP documentation here.