1. A machine implemented method for implementing model definition, constraint enforcement, and validation, the method being performed by at least a client computing device and comprising: a client computing device requesting a reference to one or more model definition resources for a representation of a model that pertains to a tax preparation or financial management software application at least by transmitting a request for the reference to a remote host computer hosting the tax preparation or financial management application via a network element; the client computing device executing a model definition resolver, residing on and stored at least partially in memory of the client computing device, that identifies or determines one or more actual locations for the one or more model definition resources at least by resolving the reference and retrieving the one or more model definition resources from the one or more actual locations, wherein the one or more model definition resources specify constraints for constraint enforcement or validation on the model; the client computing device reducing data processing and data to be populated into the model at least by removing a portion of the data and populating a remaining portion of the data into the model through using one or more validation modules and one or more formatting modules stored at least partially in the memory of the client computing device, the client computing device reducing the data processing and the data comprising: disabling the constraint enforcement or validation for a portion of a flow of the tax preparation or financial management application; reducing a total number of data elements and a total number of invalid data elements at least by formatting one or more user inputs for the tax preparation or financial management application at the one or more formatting modules; and performing the constraint enforcement or validation at the one or more validation modules on at least the one or more user inputs, which have been formatted, based in part or in whole upon at least the one or more model definition resources obtained by the model definition resolver residing on the client computing device from the remote host computer via the network element; and the client computing device performing data binding for the data to bind the data to the model by using a first application programming interface located on the client computing device, further comprising; the client computing device identifying a model definition for a requested key of a key-value pair for the data and obtaining an actual implementation of the one or more model definition resources from the remote host computer by processing the reference with a mapping module; the client computing device generating a first result at least by determining whether the requested key for the data is allowed in the model based at least in part upon the actual implementation of the one or more model definition resources and further generating a second result at least by determining whether a requested value of the key-value pair for the data matches the model definition; and the client computing device performing the data binding for the data and the model based at least in part upon the first result and the second result.