1. A prescriptive modular service oriented architecture (SOA) to obtain reusable services in a computing system, said reusable services being composed into service oriented multiple processes and composite solutions on web-application, said prescriptive SOA comprising: a plurality of tiers in the computing system selectively including a client tier; a presentation tier; a business logic tier; an integration tier; and a data tier; and an infrastructure service layer in the computing system designed across and interacting with said plurality of tiers, wherein the infrastructure service layer is configured to provide configurable services reusable by all said plurality of tiers by invoking them through a common invocation framework (CIF), wherein the configurable services include multiple implementations of the reusable services, and wherein the CIF facilitates dynamic discovery of an implementation of a reusable service from the configurable services registered on a registry in the infrastructure service layer and dynamically invokes, a discovered implementation of the reusable service upon receiving a request, through a service broker; wherein said data tier includes persistence logic to interact with underlying data stores, and data models representing data entities as objects, and a data access layer which encapsulates details connecting data models to the data stores; the integration tier is configured to provide services needed for providing interfacing with external systems; and the presentation tier is configured to implement data validations, to maintain a conversational state, and to provide infrastructure capabilities including caching viewable information, authenticating and authorizing users.