1. A method, comprising: through an application program interface, receiving from an advertiser input data defining an advertising campaign of the advertiser, the advertising campaign including one or more contracts, each respective contract defining one or more advertising placements, each respective advertising placement being associated with one or more predicate configurations; using the input data defining the advertising campaign, constructing, by an index construction module, in electronic memory, a targeting dimension dictionary that is user extensible to new attribute type declarations, the targeting dimension dictionary comprising at least three targeting dimensions including a dimension of web pages, each targeting dimension comprising at least two attribute types, each attribute type comprising one or more attribute values to make the targeting dimension dictionary scalable and extensible to newly added attribute type declarations and number of values against each attribute type, and the targeting dimension dictionary comprising a history of hits associated with the attribute values; receiving from a user advertiser input data defining a new targeting dimension, a new dimension attribute type or a new dimension attribute value corresponding to new targeting criteria introduced by the user; dynamically updating the targeting dimension dictionary, using the index construction module, by adding at least one of the new targeting dimension, the new dimension attribute type, or the new dimension attribute value based on the advertiser input data provided by the user, without modifying the application programming interface, the one or more contracts including one or more newly added attribute type declarations or number of values against each attribute type; generating, using a campaign authoring tool and based on clauses of a contract, a target predicate for the contract, at least in part using the updated targeting dimension dictionary, wherein the target predicate for the contract is amalgamated with one or more other target predicates of a predicate configuration of the one or more predicate configurations; determining, by a predicate configuration manager module, whether the target predicate for the contract covers a target market based on the history of hits associated with the attribute values; adjusting, by the predicate configuration manager module, the target predicate when the target predicate for the contract does not cover a target market; identifying an impression available for booking at a web page of the web pages; generating, by the predicate configuration manager module, a placement opportunity profile predicate for the impression, at least in part using the targeting dimension dictionary, the placement opportunity profile predicate being generated based on dimension attributes of the history of hits for the web page; determining whether the target predicate matches the placement opportunity profile predicate; responsive to the target predicate being matched to the placement opportunity profile predicate, booking, in the electronic memory, an advertisement associated with the contract to the impression associated with the placement opportunity profile predicate, and serving the advertisement associated with the contract to the impression to a client system over a network.