1. A computer-implemented method of providing access to data having a particular schema, comprising: providing a data abstraction model which models the data having the particular schema and exposes the data to users in a manner that allows the users to compose abstract queries on the basis of the data abstraction model without knowledge of the particular schema; wherein the data abstraction model comprises a plurality of logical field definitions, the plurality of logical field definitions being maintained separately from physical queries, each of the logical field definitions comprising: (i) a logical field name; (ii) at least one location attribute identifying a location of physical data corresponding to the logical field name; and (iii) a reference to an access method for accessing the physical data in response to receiving the abstract query containing the logical field name, wherein at least one of the logical field names is different from a physical field name of the corresponding physical data as defined by the schema; and configuring one or more computer processors to perform an operation comprising: receiving an abstract query that is expressed according to a syntax of a predefined query language, comprising: (i) a user-specified result specification specifying one or more logical field definitions for which results are to be returned; and (ii) at least one user-specified selection criterion specifying conditions to filter the physical data corresponding to the one or more logical field definitions specified by the result specification; and accessing the data abstraction model in response to receiving the abstract query, wherein accessing comprises: invoking an access method of one of the one or more logical field definitions to access the physical data.