Explanation/Reference:
Some minor modifications may be required to support connectivity, but requiring extensive modifications defeats a major reason for integration.
It must be noted that creating a SOA Service from existing assets generally requires a good deal more than just adding a standards-based interface, i.e. simply service enabling existing assets is insufficient.
The SOA Service needs to expose process, functionality, and data that is usable in a broader context than the source of the capability was designed to meet. Therefore, creating a SOA Service usually entails some amount of aggregation, transformation, or expansion of existing capabilities provided by the source systems. This requires a SOA Services layer between the existing assets and the consumers as illustrated in the figure.

Note: The primary goal of service-oriented integration is to better leverage existing systems within the IT environment by applying service-oriented principles. Ultimately, the goal is to enable the assembly of composite applications, with little or no custom coding, that include capabilities sourced from existing systems.
Composite applications are applications that pull together data, functionality, and process from multiple existing sources to solve a business problem or create new business value.
Service-oriented integration is the mechanism to expose existing sources of data, functionality, and process so that those sources can be readily consumed by a composite application.
Service construction includes creating entirely new SOA Services and also exposing existing assets as SOA Services.
Reference: Oracle Reference Architecture, Service-Oriented Integration, Release 3.0