9. Apparatus for text processing, comprising: an interface, which is operative to accept a body of text, which originates from audio of call center sessions and comprises semantic elements; and a processor, which is coupled to process the body of text so as to recognize respective syntactic roles of the semantic elements, to segment the body of text into individual semantic constructs responsively to the recognized syntactic roles, wherein syntactic roles of the different semantic elements are represented by a given sentence as a hierarchical structure such as a tree, having subordinate and superordinate branches connected at nodes, to remove selected semantic elements from the semantic constructs so as to transform the semantic constructs into respective nuclear semantic constructs, to compute respective occurrence frequencies of the nuclear semantic constructs, to aggregate similar nuclear constructs, so that frequently occurring nuclear constructs are given high statistical significance; and to invoke an action with respect to one or more of the nuclear semantic constructs whose occurrence frequencies meet a predefined condition, wherein the processor is coupled to accept a definition of a nuclearization depth, and to determine the selected semantic elements to be removed responsively to the nuclearization depth wherein the processor is coupled to assign respective weights to occurrences of the nuclear semantic constructs and to compute the occurrence frequencies responsively to the weights.
10. The apparatus according to claim 9 , wherein the processor is coupled to prioritize at least some of the nuclear semantic constructs and to present the prioritized nuclear semantic constructs to a user.