Consider a distributed database of video files, where each video file is annotated by keywords (i.e. text). Retrieval is

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Consider a distributed database of video files, where each videofile is annotated by keywords (i.e. text). Retrieval is thenachieved by using an inverted index that maps keywords to the videofiles (annotated by those keywords). There is no scoring or rankingand all file matching a search query will be returned.
When a single word query is issued, it is looked up independentlyon thousands of servers each holding a part of the database. Eachserver returns a list of matching video files. State briefly howthis retrieval can be achieved using map and reduce. Explain howyour solution can be extended for a multi-word query. Argue thatthe solution is scalable in both cases. If there are limitation toscalability explain them.