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| dev:technologies [2011/04/21 14:50] – [XPath] rmzelle | dev:technologies [2017/12/12 04:56] (current) – removed sean |
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| A very brief introduction to some commonly used technologies used in translator development. | |
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| ====== XPath ====== | |
| XPath provides a way to refer to specific parts of HTML or XML documents. It's usually the best way to extract data from webpages when writing a translator. | |
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| An XPath expression is a chain of pieces that specify the path to a node of the document. The main pieces of expressions are: | |
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| * ''/'' Separator between parts of the path | |
| * ''*'' match any tag | |
| * ''%%//%%'' one or more levels deeper | |
| * ''..'' go up one level | |
| * ''[]'' match a tag that has this (the contents of the brackets) | |
| * ''@key'' an attribute named ''key'' | |
| * ''text()'' match a text node | |
| * ''[2]'' match the second matching node | |
| * ''[last()]'' match the last matching node | |
| * ''div[@class="important"]'' match a ''<div>'' with the attribute ''class'', with the value ''important''. | |
| * ''td[contains(text(),"Expect")]'' match a ''<td>'' which contains text that contains "Expect" | |
| * Plus much more. See the [[http://www.w3.org/TR/xpath/|XPath specification]] and the [[https://developer.mozilla.org/en/xpath|XPath documentation]] of the Mozilla Developer Network. | |
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| The best introduction to XPath for use in translators is Mozilla's [[https://developer.mozilla.org/en/Introduction_to_using_XPath_in_JavaScript|Introduction to using XPath in JavaScript]], but it may be even easier to model your code off of the logic in existing translators, which provide a wide array of XPath techniques to pick apart fussy sites. | |
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| === Examples === | |
| <code html> | |
| <div id="names"> | |
| <span class="editor">George Spelvin</span>, | |
| <span class="translator">Andrea Johnson</span> | |
| </div> | |
| <table> | |
| <tr class="odd"> | |
| <td>Great Expectations</td> | |
| <td>Mediocre Plans</td> | |
| </tr> | |
| </table> | |
| </code> | |
| For the sample document above, these expressions would refer to... | |
| * ''%%//tr[@class="odd"]/td%%'': a result set with the nodes ''<td>Great Expectations</td>'' and ''<td>Mediocre Plans</td>'' | |
| * ''%%//table//td%%'': Same as previous | |
| * ''%%//span[@class="editor"]%%'': a result set with the single node ''<span class="editor">George Spelvin</span>'' | |
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| ====== Regular Expressions ====== | |
| * ''.'' matches any character | |
| * ''[a-z01]'' matches any of the lowercase English letters and the numbers 0 and 1 | |
| * ''()'' surround a match expression | |
| * ''+'' Match one or more of the preceding expression | |
| * ''*'' Match 0 or more of the preceding expression | |
| * ''?'' Match 0 or 1 of the preceding expression | |
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