According to the proposal of Document Standardization Center of National Library: Subject Indexing Rules of China Library-Basic Volume (GB/T 22205-2008), each subject indexing should include a subject word and several non-subject words. According to the international thesaurus and other related materials provided by the National Library, some keywords can be used to index the themes of the three-body system, such as alien civilization, cosmic civilization, clash of civilizations, artificial intelligence, science fiction and so on.
It should be noted that subject indexing is a convenient method for readers to find and retrieve relevant documents, so when compiling indexing, it is necessary to make appropriate supplements and revisions in combination with the specific plot of the work and the fields involved in the subject.