Manage internal and external interface definitions, designs, and changes for service systems.


Many integration problems arise from unknown or uncontrolled aspects of both internal and external interfaces. Effective management of interface requirements, specifications, and designs helps to ensure that implemented interfaces will be complete and compatible.

In the context of service systems, interfaces can be broadly characterized according to one of four major groups:

  • Person-to-person interfaces are interfaces that represent direct or indirect communication between two or more people, any of whom might be service provider staff or end users. For example, a call script, which defines how a help desk operator should interact with an end user, defines a direct person-to-person interface. Log books and instructional signage are examples of indirect person-to-person interfaces.
  • Person-to-component interfaces are interfaces that encompass interactions between a person and one or more service system components. These interfaces can include both graphical user interfaces for automated components (e.g., software applications), and operator control mechanisms for automated, partially automated, and non-automated components (e.g., equipment, vehicles).
  • Component-to-component interfaces are interfaces that do not include direct human interaction. The interfaces of many interactions between automated components belong to this group but other possibilities exist, such as specifications constraining the physical mating of two components (e.g., a delivery truck, a loading dock).
  • Compound interfaces are interfaces that merge or layer together interfaces from more than one of the other three groups. For example, an online help system with “live” chat support might have a compound interface built on an integrated combination of person-to-person, person-to-component, and component-to-component interfaces.

Interfaces can also be characterized as external or internal interfaces. “External interfaces” are interactions among components of the service system and any other entity external to the service system, including people, organizations, and systems. Internal interfaces can include the interactions among the staff, teams, and functions of the service provider organization. “Internal interfaces” can also include interaction between the staff or end users and service system components.


Examples of user interface work products include the following:
  • Customer interaction scripts
  • Reporting types and frequency
  • Application program interfaces

Example Work Products

  1. Categories of interfaces with lists of interfaces per category
  2. Table or mapping of interface relationships among service system components and the external environment
  3. List of agreed interfaces defined for each pair of service system components when applicable
  4. Reports from meetings of the interface control working group
  5. Action items for updating interfaces
  6. Updated interface description or agreement


1. Review interface descriptions for coverage and completeness.

The interface descriptions should be reviewed with relevant stakeholders to avoid misinterpretations, reduce delays, and prevent the development of interfaces that do not work properly.

2. Manage internal and external interface definitions, designs, and changes for service system components.

Management of the interfaces includes maintenance of the consistency of the interfaces throughout the life of the service system, compliance with architectural decisions and constraints, and resolution of conflict, noncompliance, and change issues. It is also important to manage the interfaces between components acquired from suppliers and other service system components.