How to Validate an Element in an XML File
Using XML data within an application is typically a straightforward process. However, in order to produce XML that is going to be reliable, it is necessary to ensure that it is well-formed. Validating XML helps to eliminate errors. However, the validation process itself does not fix errors, it simply highlights them so that you, as a developer, can address them. The W3Schools website is the main source used for validating XML; however, there are other sites and some software applications which perform the same function.
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Instructions
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Prepare your XML data. The following is an example of an XML document:
<?xml version="1.0"?>
<book>
<title>The Lovely Picnic</title>
<author>Mary Smith</author>
</book>
This XML data contains a root element with two child elements. Validating your XML elements involves the same process regardless of the structures they contain.
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Browse to the W3Schools XML Validator page in a Web browser. The simplest way to validate your XML elements is by copying and pasting them into the page text-area section entitled "Syntax-Check Your XML." Open the document containing the XML you want to validate, select all of it by pressing "Ctrl+A" or "Command-A" on a Mac. Copy the XML by pressing "Ctrl+C" or "Command-C" on a Mac. Paste the XML into the validation Web page by clicking within the text-area, deleting any existing content, and then pressing "Ctrl+V" or "Command-V" on a Mac.
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Validate your XML data. Click the "Validate" button. If your XML does not contain any errors, an alert box will appear displaying a confirmation that no errors have been found. If there are errors, an alert box will appear, initially describing the first error encountered. If this happens, read the message displayed and locate the error within your XML document. The error message will describe the type of error and the detail of any tags involved in it, as well as the line number and location at which it occurs.
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Fix any errors highlighted by the validator. When you receive an error message, find the location in your file where it appears, alter your XML markup to correct it and save your document. Copy the XML content and paste it into the validator again. The validator works by stopping when it encounters a single error. This means that fixing this error does not necessarily mean that your XML is now completely free of errors. When you paste the amended XML content back into the validator you may receive further errors. Fix each one in turn and continue validating until you receive an alert indicating that the XML no longer contains any errors.
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Validate your XML using a DTD. This is optional and is only relevant if you are using a DTD. DTDs (Document Type Definitions) dictate the structures that a set of XML data is allowed to contain. If you are using one, scroll down the validation Web page to the "Validate Your XML Against a DTD" section and enter the text of your DTD together with the XML content. Click the "Validate" button to check your XML for errors.
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Tips & Warnings
Using software that highlights XML content makes mark-up errors far less likely, as many of them are highlighted or corrected as you type.
Validating an XML document does not necessarily mean that it will function correctly within a larger application, as this depends partly on the other technologies involved.
References
Resources
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