1. A task-based advertisement system comprising a computer that comprises a processor that executes computer-executable instructions that cause the computer to implement a task server that: selects, based upon the tokens in a query from a user, a task from among a plurality of tasks, each task in the plurality of tasks being an action relevant to users of a search engine, each task in the plurality of tasks specifying multiple slots that define parameters of the task into which tokens in queries can be filled; after selecting the task, generates a semantic solution that represents a mapping between the slots of the task and tokens in the query that fill the slots of the task, wherein the task server generates the semantic solution at least in part by: identifying an annotation token among the tokens in the query, the annotation token being a token that indicates a significance of a subject token, the subject token being another one of the tokens in the query; and determining, based at least in part on the significance of the subject token, whether the subject token should be mapped in a given one of the slots of the task; and after generating the semantic solution, provides data representing the task, along with the semantic solution, to search engine, wherein the search engine provides the task to an advertiser computer that determines whether to make a bid on the task based at least in part on the semantic solution.