CWA 16374-1:2011

Extensions for Financial Services (XFS) interface specification Release 3.20 - Part 1: Application Programming Interface (API) Service Provider Interface (SPI) Programmer's Reference

Scope

This document provides the technical specifications for the CEN/ISSS eXtensions for Financial Services (referred to hereafter as “XFS” for brevity).
In this specification, the functions of the XFS Application Programming Interface (API) and Service Provider Interface (SPI) are always described in terms of providing a standardized, portable interface for applications to gain access to Service Providers. This architecture allows Service Providers to deliver an open-ended set of capabilities to financial applications based on the Microsoft Windows operating systems, including access to peripheral devices unique to financial institutions. Since the first priority of the CEN members for XFS implementations has been to provide this peripheral device access capability, the examples used relate primarily to device control and physical input/output.
The key elements of the Extensions for Financial Services are the API definition and the corresponding SPI definition, used by the XFS Manager to communicate with the Service Providers, together with the set of supporting services provided by the XFS Manager. These elements are combined in an XFS implementation, providing access to financial devices and services for Windows-based applications.
The specification defines a standard set of interfaces in order to provide multi-vendor interoperability: if an application uses the API to communicate successfully with a Service Provider, it should work with another conformant Service Provider of the same type, developed by another vendor, without any changes. To work with more than one hardware implementation of a device, an application must retrieve the device capability information - this will allow the application to successfully interact with different variants of the same hardware device. Applications that use the vendor specific fields of XFS commands may not be able to interact successfully with another vendor’s conformant Service Provider. Applications should isolate vendor specific access to devices in order to maximize consistent device control across multiple device Service Provider implementations. Any Service Provider that conforms to the SPI definition can work with a range of conformant applications.
As new versions of the XFS device classes are developed and released, changes to the device class interface specifications are inevitable. Application exposure to these changes is controlled via the version negotiation process described later in this specification. Applications need to be updated to support new releases of XFS, but to minimize the migration effort it is recommended that they should be developed in such a way that they can handle additional error codes and new output literal values being added to existing commands within future versions of XFS in a graceful manner. In addition, applications must release the memory for all events received, this includes events that the application may be unaware at development time, i.e. the minimum processing for any XFS event must be the release of the memory associated with the event.