c468.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML
><HEAD
><TITLE
>Package hdom</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.77"><LINK
REL="HOME"
TITLE="Design and Implementation of a validating XML parser in Haskell"
HREF="index.html"><LINK
REL="PREVIOUS"
TITLE="Haskell"
HREF="x298.html"><LINK
REL="NEXT"
TITLE="Data structures"
HREF="x558.html"></HEAD
><BODY
CLASS="chapter"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Design and Implementation of a validating XML parser in Haskell: Master's thesis; 
			University of Applied Sciences Wedel
		</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x298.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x558.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="chapter"
><H1
><A
NAME="c2"
></A
>Chapter 2. Package hdom</H1
><P
>&#13;	This chapter describes the package <TT
CLASS="filename"
>hdom</TT
>, which defines a generic tree data type <TT
CLASS="literal"
>XmlTree</TT
> for representing whole XML documents in Haskell. The package provides many functions for processing XML documents represented by this data model.
	</P
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="modules"
></A
>2.1. Modules</H1
><P
>&#13;		The core public module of the package <TT
CLASS="filename"
>hdom</TT
> is the module <TT
CLASS="classname"
>XmlTree</TT
>. It exports all elements from the basic libraries <TT
CLASS="classname"
>XmlTreeAccess</TT
>, <TT
CLASS="classname"
>XmlTreePredicates</TT
>, <TT
CLASS="classname"
>XmlTreeTypes</TT
>, <TT
CLASS="classname"
>NTree</TT
> and <TT
CLASS="classname"
>XmlKeywords</TT
>.
		</P
><P
>&#13;		The module <TT
CLASS="classname"
>XmlTreeTypes</TT
> defines data types for representing any XML document in Haskell. The generic tree data type <TT
CLASS="literal"
>XmlTree</TT
> models XML documents, including all logical units of XML like the DTD subset or document subset. This type is based on the general n-ary tree <TT
CLASS="literal"
>NTree</TT
> defined in the module <TT
CLASS="classname"
>NTree</TT
>. The type <TT
CLASS="literal"
>NTree</TT
> defines trees as a node that has a list of child nodes. Leafs are just nodes with an empty child list. XML documents are composed of elements, comments, DTD declarations, character references or processing instructions. <TT
CLASS="literal"
>XmlTree</TT
> provides for each logical unit an own node type.
		</P
><P
>&#13;		The module <TT
CLASS="classname"
>NTree</TT
> defines a general n-ary tree structure <TT
CLASS="literal"
>NTree</TT
> as well as filter functions (see  <A
HREF="x854.html"
>Section 2.3</A
>) and combinators (see  <A
HREF="x1178.html"
>Section 2.4</A
>) for processing this data type. The filters and combinators have been copied and modified from HaXml [<SPAN
CLASS="citation"
><A
HREF="b2463.html#bib_haxml"
><SPAN
CLASS="abbrev"
>WWW21</SPAN
></A
></SPAN
>]. In contrast to HaXml the filters have been modified using a more generic approach. The filter functions of HaXml work only for the document subset of XML documents. Because of the generic tree data model <TT
CLASS="literal"
>NTree</TT
> these functions can be used to process whole XML documents in the Haskell XML Toolbox.
		</P
><P
>&#13;		The module <TT
CLASS="classname"
>XmlTreeAccess</TT
> provides basic filter functions for constructing, editing or selecting parts of the data type <TT
CLASS="literal"
>XmlTree</TT
>. Furthermore it provides functions for processing the attribute list of <TT
CLASS="literal"
>XmlTree</TT
> nodes.
		</P
><P
>&#13;		The module <TT
CLASS="classname"
>XmlTreePredicates</TT
> provides basic predicate filter functions. The functions are similar to predicate logic. If the condition is true, they return a list with a node, otherwise they return an empty list.
		</P
><P
>&#13;
		The module <TT
CLASS="classname"
>XmlKeywords</TT
> provides constants that are used for representing DTD keywords and attributes in the <TT
CLASS="literal"
>XmlTree</TT
>.
		</P
><P
>&#13;        	<DIV
CLASS="figure"
><A
NAME="modules_xmltree"
></A
><P
><B
>Figure 2-1. Module hierarchy of XmlTree</B
></P
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="images/modules_xmltree.gif"></P
></DIV
></DIV
>
        </P
><P
>&#13;		Besides the module <TT
CLASS="classname"
>XmlTree</TT
> and its sub-modules there exist some other public modules for processing the <TT
CLASS="literal"
>XmlTree</TT
> data structure.
		</P
><P
>&#13;		<TT
CLASS="classname"
>XmlTreeToString</TT
> provides functions for transformation of an <TT
CLASS="literal"
>XmlTree</TT
> back into a string. The string shows an XML document in XML syntax.
		</P
><P
>&#13;		<TT
CLASS="classname"
>EditFilters</TT
> provides some filters for transforming an <TT
CLASS="literal"
>XmlTree</TT
>:
		</P
><P
></P
><UL
><LI
><P
>Remove text nodes which contain only white space from the tree.</P
></LI
><LI
><P
>Remove comment nodes from the tree.</P
></LI
><LI
><P
>Transform special characters like &#60;, &#62;, ", ' and &#38; of text nodes into character references.</P
></LI
><LI
><P
>Manipulate text nodes with customized functions.</P
></LI
><LI
><P
>Convert CDATA nodes to text nodes by escaping all special characters.</P
></LI
><LI
><P
>Convert character references to normal text.</P
></LI
><LI
><P
>Create a canonicalized representation of XML documents [<SPAN
CLASS="citation"
><A
HREF="b2463.html#bib_canxml"
><SPAN
CLASS="abbrev"
>WWW03</SPAN
></A
></SPAN
>].</P
></LI
></UL
><P
>&#13;		<TT
CLASS="classname"
>FormatXmlTree</TT
> creates a string with a tree representation of an <TT
CLASS="literal"
>XmlTree</TT
>. This is useful to see how the data type <TT
CLASS="literal"
>XmlTree</TT
> represents an XML document.
		</P
><P
>&#13;		<TT
CLASS="classname"
>XmlFilterCombinators</TT
> provides special filter combinators for processing an <TT
CLASS="literal"
>XmlTree</TT
>. These filters can only operate on the data type <TT
CLASS="literal"
>XmlTree</TT
> and not on the general n-ary tree data type <TT
CLASS="literal"
>NTree</TT
>.
		</P
><P
>&#13;        	<DIV
CLASS="figure"
><A
NAME="modules_hdom"
></A
><P
><B
>Figure 2-2. General modules of package hdom</B
></P
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="images/modules_hdom.gif"></P
></DIV
></DIV
>
        </P
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x298.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x558.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Haskell</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
>&nbsp;</TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Data structures</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>