The battle between Google and Oracle over the Java programming language is heating back up.

Last year, a federal court decided in favor of Google after Oracle sued the web giant over its use of Java. But yesterday, the U.S. Court of Appeals for the Federal Circuit questioned Google as part of Oracle's appeal of the ruling, and it indicated that the decision could be overturned, according to a report from Reuters.

In August of 2010 – after acquiring Sun Microsystems, the maker of Java – Oracle sued Google, claiming the web giant infringed on various Java-related copyrights and patents in building Android. At the core of its argument was the claim that Google had illegally cloned 37 APIs, or applications programming interfaces, that coders use to build Java apps. Google did clone the APIs – the idea was to build a new version of the Java software platform that runs applications written in the Java programming language – but the company always contended that the code used to clone these APIs was its own.

The judge originally assigned to the case, Judge William Alsup, went so far as to learn the Java programming language to better understand the technical details of the case, and he eventually concluded that APIs could not be copyrighted. He said that the Java APIs were kinda like the method you would use to organize a library of books, saying that you can copyright the content of the books on a shelf, but not the way they are organized.

Oracle disagreed, and filed an appeal in February, arguing that Google's use of the Java API was akin to copying the chapter titles and topic sentences of a Harry Potter novel verbatim, paraphrasing the rest, and then trying to pass the whole thing off as an original work.

"I think the legal strategy is right, if they want to win the case,” Ed Walsh, an intellectual property attorney with the Boston-based law firm Wolf Greenfield told us at the time.

Oracle is asking for about $1 billion in damages from Google, but if the original decision is reversed, it could also have major ramifications for the entire software industry. Many open source software projects rely on APIs cloned from other systems to ensure compatibility and reduce learning curves. For example, Cisco's private cloud system CloudStack and Basho's RiakCS file system mimic the Amazon Web Services API.

If the appeals court decides in Oracle's favor, Google could in turn appeal that decision, potentially elevating the case to the Supreme Court.

API evangelist Kin Lane has stated that it's important for the tech industry to standardize on open APIs instead of ones that may be jealously guarded by copyright trolls. His site API Commons, launched in conjunction with 3Scale last month, provides a place for companies and individuals to share API designs under common licenses much the same way developers already share open source code.

Openly licensed APIs will be a good thing, but it may be hard for developers to wean themselves off major APIs from Oracle and Amazon. That's why this court decision is still so important.