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If you file your income tax electronically, you've already done what we expect: You've used some software to do a detailed report and submitted it as an XML file where it's written directly into a database. That's what an ONIX file is, a file that is used by retailers and others to directly fill their databases with information. If it's right and machine readable, and contains everything another business needs and a consumer needs to make a buying decision then potential sales happenare fully supported. You probably can't do taxes without some research – but you can rely on the tax software to help you. For book metadata you'll need to understand what other business need from you, and ONIX software can help in some of that but mainly it will ensure the file is machine readable.
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ONIX Usage -- A guide to BNC Webform Data Entry and Code list references
Finding and Using the ONIX Manual and Code Lists