1. A method for evaluating applicability of a data set for a target project estimation, the method comprising: defining a collection of reference data sets derived from multiple historical projects in a similar subject area as the target project; defining multiple indicators of data set applicability to a target project estimation, wherein each of said multiple indicators is based on a characteristic specific to the target project, and wherein the multiple indicators comprise: a degree of coherence of target project environment variables across the multiple historical projects; a degree of evenness of project size distribution across the multiple historical projects; a degree of uncertainty attributed to of each of the reference data sets; and a sufficiency of a total number of historical projects in each of the reference data sets determined by comparing a number of historical projects in each reference data set to a threshold number of historical projects; determining a set of governance rules to be associated with the multiple indicators to determine relevance of historical projects in each of the reference data sets to the target project estimation, wherein said set of governance rules comprises (i) one or more rules derived from characteristics of the target project and (ii) one or more rules based on characteristics of an execution environment for which the target project estimation is to be carried out, wherein said determining comprises: establishing a communicative link between a project plan database and a project characteristic extraction module executing on a hardware processor of the computing device; extracting multiple characteristics of the target project from the project plan database via the project characteristic extraction module; and selecting the set of governance rules from the project plan database based on (i) characteristics of the execution environment for which the target project estimation is to be carried out (ii) the multiple extracted characteristics of the target project, wherein said selecting is carried out by a rule selection module executing on the hardware processor of the computing device and communicatively linked to the project plan database and the project characteristic extraction module; evaluating applicability of each of the reference data sets to the target project by ill applying the set of governance rules and (ii) determining an alignment of each of the reference data sets to each of the multiple indicators, wherein said evaluating is carried out by an evaluation module executing on the hardware processor of the computing device and communicatively linked to the collection of reference data sets and the rule selection module; and identifying one or more of the reference data sets as applicable for use in the target project estimation.