An  Application Interface is a Business Service Interface that occurs between Business Software Systems.

The interface is described by messages exchanged between endpoints (provider, consumer..).

An  Physical Software Interface is a physical specification of an Application Interface to which it adds the following physical characteristics:

1) The software communication protocol which defines the format of the data, the procedures for error handling, and the protocols for data transfer. Examples of software communication protocols include HTTP, SOAP, gRPC,

2) Potential specific target port number.

3) Optional restrictions on source port number to use .

4) Transport protocol (TCP/UDP).

 Physical Software Interfaces can also represent lower lever APIs supported by Software Technology Systems such as DHCP, SMTP, IMAP, LDAP.

A  Business Software System is a Business System used by Business Operations, that represents all granularities of software - ranging from MicroServices to enterprise wide Application Systems - used by Business Operations.

All  Business Software Systems share the following characteristics:

1) They provide  Functionalitys.

2) They expose APIs (Application Interfaces) through which they deliver Information Outcome Events.

3) They handle datastores defined by Physical Data Domains.

4) They perform and participate to System Processes.

A  Computing System is a system that can host and run software code ( Application code or Software Technology code) and to host data.

Examples: Computer Devices, Computer Servers, Cloud Services.