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1 <?xml version="1.0" encoding="UTF-8"?> |
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26 |
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27 <!DOCTYPE html |
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28 PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" |
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29 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> |
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30 |
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31 <html xmlns="http://www.w3.org/1999/xhtml"> |
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32 |
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33 <head> |
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34 <title>Transformation API For XML</title> |
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35 |
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36 <meta name="CVS" |
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37 content="$Id: overview.html,v 1.2 2005/06/10 03:50:39 jeffsuttor Exp $" /> |
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38 <meta name="AUTHOR" |
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39 content="Jeff.Suttor@Sun.com" /> |
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40 </head> |
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41 <body> |
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42 |
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43 <h2>Transformation API For XML</h2> |
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44 |
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45 |
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46 <h3>Introduction</h3> |
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47 |
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48 <p>This overview describes the set of APIs contained in |
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49 javax.xml.transform. For the sake of brevity, these interfaces are referred to |
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50 as TrAX (Transformations for XML). </p> |
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51 |
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52 <p>There is a broad need for Java applications to be able to transform XML |
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53 and related tree-shaped data structures. In fact, XML is not normally very |
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54 useful to an application without going through some sort of transformation, |
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55 unless the semantic structure is used directly as data. Almost all XML-related |
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56 applications need to perform transformations. Transformations may be described |
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57 by Java code, Perl code, <A href="http://www.w3.org/TR/xslt">XSLT</A> |
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58 Stylesheets, other types of script, or by proprietary formats. The inputs, one |
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59 or multiple, to a transformation, may be a URL, XML stream, a DOM tree, SAX |
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60 Events, or a proprietary format or data structure. The output types are the |
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61 pretty much the same types as the inputs, but different inputs may need to be |
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62 combined with different outputs.</p> |
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63 |
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64 <p>The great challenge of a transformation API is how to deal with all the |
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65 possible combinations of inputs and outputs, without becoming specialized for |
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66 any of the given types.</p> |
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67 |
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68 <p>The Java community will greatly benefit from a common API that will |
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69 allow them to understand and apply a single model, write to consistent |
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70 interfaces, and apply the transformations polymorphically. TrAX attempts to |
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71 define a model that is clean and generic, yet fills general application |
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72 requirements across a wide variety of uses. </p> |
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73 |
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74 |
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75 <h3>General Terminology</h3> |
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76 |
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77 <p>This section will explain some general terminology used in this |
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78 document. Technical terminology will be explained in the Model section. In many |
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79 cases, the general terminology overlaps with the technical terminology.</p> |
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80 |
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81 <ul> |
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82 <li> |
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83 <p> |
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84 <b>Tree</b> |
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85 <br>This term, as used within this document, describes an |
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86 abstract structure that consists of nodes or events that may be produced by |
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87 XML. A Tree physically may be a DOM tree, a series of well balanced parse |
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88 events (such as those coming from a SAX2 ContentHander), a series of requests |
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89 (the result of which can describe a tree), or a stream of marked-up |
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90 characters.</p> |
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91 </li> |
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92 <li> |
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93 <p> |
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94 <b>Source Tree(s)</b> |
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95 <br>One or more trees that are the inputs to the |
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96 transformation.</p> |
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97 </li> |
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98 <li> |
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99 <p> |
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100 <b>Result Tree(s)</b> |
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101 <br>One or more trees that are the output of the |
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102 transformation.</p> |
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103 </li> |
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104 <li> |
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105 <p> |
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106 <b>Transformation</b> |
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107 <br>The processor of consuming a stream or tree to produce |
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108 another stream or tree.</p> |
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109 </li> |
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110 <li> |
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111 <p> |
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112 <b>Identity (or Copy) Transformation</b> |
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113 <br>The process of transformation from a source to a result, |
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114 making as few structural changes as possible and no informational changes. The |
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115 term is somewhat loosely used, as the process is really a copy. from one |
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116 "format" (such as a DOM tree, stream, or set of SAX events) to |
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117 another.</p> |
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118 </li> |
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119 <li> |
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120 <p> |
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121 <b>Serialization</b> |
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122 <br>The process of taking a tree and turning it into a stream. In |
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123 some sense, a serialization is a specialized transformation.</p> |
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124 </li> |
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125 <li> |
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126 <p> |
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127 <b>Parsing</b> |
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128 <br>The process of taking a stream and turning it into a tree. In |
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129 some sense, parsing is a specialized transformation.</p> |
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130 </li> |
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131 <li> |
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132 <p> |
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133 <b>Transformer</b> |
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134 <br>A Transformer is the object that executes the transformation. |
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135 </p> |
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136 </li> |
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137 <li> |
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138 <p> |
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139 <b>Transformation instructions</b> |
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140 <br>Describes the transformation. A form of code, script, or |
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141 simply a declaration or series of declarations.</p> |
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142 </li> |
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143 <li> |
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144 <p> |
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145 <b>Stylesheet</b> |
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146 <br>The same as "transformation instructions," except it is |
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147 likely to be used in conjunction with <A href="http://www.w3.org/TR/xslt">XSLT</A>.</p> |
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148 </li> |
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149 <li> |
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150 <p> |
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151 <b>Templates</b> |
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152 <br>Another form of "transformation instructions." In the TrAX |
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153 interface, this term is used to describe processed or compiled transformation |
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154 instructions. The Source flows through a Templates object to be formed into the |
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155 Result.</p> |
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156 </li> |
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157 <li> |
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158 <p> |
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159 <b>Processor</b> |
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160 <br>A general term for the thing that may both process the |
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161 transformation instructions, and perform the transformation.</p> |
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162 </li> |
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163 <li> |
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164 <p> |
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165 <b>DOM</b> |
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166 <br>Document Object Model, specifically referring to the |
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167 <A href="#http://www.w3.org/TR/DOM-Level-2%20">Document Object Model |
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168 (DOM) Level 2 Specification</A>.</p> |
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169 </li> |
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170 <li> |
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171 <p> |
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172 <b>SAX</b><br> |
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173 Simple API for XML, specifically referring to the <a href="http://sax.sourceforge.net/">SAX 2.0.2 release</a>. |
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174 </p> |
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175 </li> |
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176 </ul> |
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177 |
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178 |
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179 |
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180 <h3>Model</h3> |
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181 |
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182 <p>The section defines the abstract model for TrAX, apart from the details |
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183 of the interfaces.</p> |
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184 |
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185 <p>A TRaX <A href="#pattern-TransformerFactory">TransformerFactory</A> is an object |
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186 that processes transformation instructions, and produces |
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187 <A href="#pattern-Templates">Templates</A> (in the technical |
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188 terminology). A <A href="#pattern-Templates">Templates</A> |
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189 object provides a <A href="#pattern-Transformer">Transformer</A>, which transforms one or |
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190 more <A href="#pattern-Source">Source</A>s into one or more |
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191 <A href="#pattern-Result">Result</A>s.</p> |
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192 |
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193 <p>To use the TRaX interface, you create a |
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194 <A href="#pattern-TransformerFactory">TransformerFactory</A>, |
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195 which may directly provide a <A href="#pattern-Transformers">Transformers</A>, or which can provide |
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196 <A href="#pattern-Templates">Templates</A> from a variety of |
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197 <A href="#pattern-Source">Source</A>s. The |
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198 <A href="#pattern-Templates">Templates</A> object is a processed |
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199 or compiled representation of the transformation instructions, and provides a |
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200 <A href="#pattern-Transformer">Transformer</A>. The |
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201 <A href="#pattern-Transformer">Transformer</A> processes a |
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202 <A href="#pattern-Transformer">Source</A> according to the |
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203 instructions found in the <A href="#pattern-Templates">Templates</A>, and produces a |
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204 <A href="#pattern-Result">Result</A>.</p> |
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205 |
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206 <p>The process of transformation from a tree, either in the form of an |
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207 object model, or in the form of parse events, into a stream, is known as |
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208 <code>serialization</code>. We believe this is the most suitable term for |
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209 this process, despite the overlap with Java object serialization.</p> |
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210 |
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211 <H3>TRaX Patterns</H3> |
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212 <ul> |
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213 <p> |
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214 <b><a name="pattern-Processor">Processor</a></b> |
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215 <br> |
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216 <br> |
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217 <i>Intent: </i>Generic concept for the |
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218 set of objects that implement the TrAX interfaces.<br> |
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219 <i>Responsibilities: </i>Create compiled transformation instructions, transform |
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220 sources, and manage transformation parameters and |
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221 properties.<br> |
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222 <i>Thread safety: </i>Only the Templates object can be |
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223 used concurrently in multiple threads. The rest of the processor does not do |
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224 synchronized blocking, and so may not be used to perform multiple concurrent |
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225 operations. Different Processors can be used concurrently by different |
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226 threads.</p> |
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227 <p> |
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228 <b><a name="pattern-TransformerFactory">TransformerFactory</a></b> |
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229 <br> |
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230 <br> |
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231 <i>Intent: </i>Serve as a vendor-neutral Processor interface for |
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232 <A href="http://www.w3.org/TR/xslt">XSLT</A> and similar |
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233 processors.<br> |
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234 <i>Responsibilities: </i>Serve as a factory for a concrete |
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235 implementation of an TransformerFactory, serve as a direct factory for |
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236 Transformer objects, serve as a factory for Templates objects, and manage |
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237 processor specific features.<br> |
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238 <i>Thread safety: </i>A |
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239 TransformerFactory may not perform mulitple concurrent |
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240 operations.</p> |
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241 <p> |
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242 <b><a name="pattern-Templates">Templates</a></b> |
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243 <br> |
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244 <br> |
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245 <i>Intent: </i>The |
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246 runtime representation of the transformation instructions.<br> |
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247 <i>Responsibilities: </i>A data bag for transformation instructions; act as a factory |
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248 for Transformers.<br> |
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249 <i>Thread safety: </i>Threadsafe for concurrent |
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250 usage over multiple threads once construction is complete.</p> |
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251 <p> |
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252 <b><a name="pattern-Transformer">Transformer</a></b> |
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253 <br> |
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254 <br> |
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255 <i>Intent: </i>Act as a per-thread |
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256 execution context for transformations, act as an interface for performing the |
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257 transformation.<br> |
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258 <i>Responsibilities: </i>Perform the |
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259 transformation.<br> |
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260 <i>Thread safety: </i>Only one instance per thread |
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261 is safe.<br> |
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262 <i>Notes: </i>The Transformer is bound to the Templates |
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263 object that created it.</p> |
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264 <p> |
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265 <b><a name="pattern-Source">Source</a></b> |
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266 <br> |
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267 <br> |
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268 <i>Intent: </i>Serve as a |
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269 single vendor-neutral object for multiple types of input.<br> |
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270 <i>Responsibilities: </i>Act as simple data holder for System IDs, DOM nodes, streams, |
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271 etc.<br> |
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272 <i>Thread safety: </i>Threadsafe concurrently over multiple |
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273 threads for read-only operations; must be synchronized for edit |
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274 operations.</p> |
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275 <p> |
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276 <b><a name="pattern-Result">Result</a></b> |
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277 <br> |
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278 <br> |
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279 <i>Potential alternate name: </i>ResultTarget<br> |
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280 <i>Intent: </i>Serve |
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281 as a single object for multiple types of output, so there can be simple process |
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282 method signatures.<br> |
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283 <i>Responsibilities: </i>Act as simple data holder for |
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284 output stream, DOM node, ContentHandler, etc.<br> |
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285 <i>Thread safety: </i>Threadsafe concurrently over multiple threads for read-only, |
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286 must be synchronized for edit.</p> |
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287 </ul> |
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288 |
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289 |
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290 </body> |
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291 </html> |