11. A server device, comprising: a memory device storing computer-executable instructions; and one or more processors to execute the computer-executable instructions, to: generate a list of relevant documents based on individual search terms of a search query; identify a subset of documents that are most relevant documents, to the search query, from the list of relevant documents; form a plurality of multiword substrings of the search query, each of the plurality of multiword substrings including at least two words; detect, for each of the plurality of multiword substrings, actual occurrences of the multiword substring in the subset of documents; calculate, for each of the plurality of multiword substrings generated from the search query, a value that indicates a fraction of the relevant documents in which an actual occurrence of the each substring is detected; identify, based on the detected actual occurrences of each of the plurality of multiword substrings, that words of at least one of the plurality of multiword substrings, when taken together, form a single compound unit, when identifying that words of at least one of the multiword substrings, when taken together, form a single compound unit, the one or more processors are to: determine that the calculated value associated with the at least one of the plurality of multiword substrings exceeds a threshold value associated with compound units; and identify a set of documents, the set of documents being identified based on the identified at least one of the plurality of multiword substrings.
11. A server device, comprising: a memory device storing computer-executable instructions; and one or more processors to execute the computer-executable instructions, to: generate a list of relevant documents based on individual search terms of a search query; identify a subset of documents that are most relevant documents, to the search query, from the list of relevant documents; form a plurality of multiword substrings of the search query, each of the plurality of multiword substrings including at least two words; detect, for each of the plurality of multiword substrings, actual occurrences of the multiword substring in the subset of documents; calculate, for each of the plurality of multiword substrings generated from the search query, a value that indicates a fraction of the relevant documents in which an actual occurrence of the each substring is detected; identify, based on the detected actual occurrences of each of the plurality of multiword substrings, that words of at least one of the plurality of multiword substrings, when taken together, form a single compound unit, when identifying that words of at least one of the multiword substrings, when taken together, form a single compound unit, the one or more processors are to: determine that the calculated value associated with the at least one of the plurality of multiword substrings exceeds a threshold value associated with compound units; and identify a set of documents, the set of documents being identified based on the identified at least one of the plurality of multiword substrings. 12. The server device of claim 11 , where the one or more processors are further to: refine the set of documents based on the identified at least one of the plurality of multiword substrings, where when identifying the set of documents, the one or more processors are to identify the set of documents based on the refining.