Interfaces and Complexity

1. Interfaces and Complexity • Networks are multi-threaded and inherently complex: • Software, hardware, and people with layers of tasks connected to produce the network • Interfaces: the way in which each part of the whole network is connected. Many flavors (non-exclusive): • Protocols • Plugs • Graphic User Interfaces (GUIs) • Application Programming Interfaces (APIs) • Special Purpose Languages • Basic human interaction MSIA715.02

2. Interface Types • Protocols and Communications Networks • An agreement between components about which of them can do what, to whom, and when. • Basic elements: set of messages and a set of rules. • Application Program Interfaces (APIs) • Calls, subroutines, or software interrupts that together comprise a formally specified interface • Allows a higher-level program to use lower level functions. MSIA715.02

3. Interface Types, continued • Shared memory, shared data, and middleware • Defined: any program that serves to glue together, mediate between, or enhance two separate and already existing programs. Facilitates cross-platform, distributed computing; also an API that shields developers from underlying transport protocols and operating systems. • Examples: workflow, distributed transactions, remote file or database access, distributed objects, distributed database access. • Remote procedure calls and messaging. • Method of program-to-program communications, in instances of multiplatform distributed computing; an interprocess API whose strength is communications between different platforms. MSIA715.02

4. Interface Types, continued • Messaging: • Defined: a loosely-coupled method of communication between platforms which uses mailboxes rather than RPCs. • Two levels are defined: • simple MAPI (messaging API) - this will perform basic mail functions such as sending and receiving messages. • Extended MAPI- this has service provider interface (SPI), which will interface to software, which in turn provides an interface to other mail services, such as Compuserve. In this way, any application using the extended MAPI will be able to use Compuserve as a message carrier. MSIA715.02

5. Selecting the Right Interface • “Poor interface design is fairly evident when, for instance a human uses a badly designed information system. When the interfaces are more deeply embedded and deal with computer-to-computer interaction, problems tend to be less obvious.” • “The variety of ways in which computer systems can be plugged together through interfaces provides something quite special - flexibility. With each of the components behind the interface created using programming languages, we can get computer-based systems to perform an infinite range of functions.” MSIA715.02

6. The Design Problem • Requirements: • Interface must specify the allowable transactions that two communicating systems can undertake. To achieve this, a mapping must be defined between the datasets of each system and the protocols used. • Design has to accommodate all states, sequences, and configurations. • “Establish a meaningful and accurate dialog between components.” • The Interface Equation: • (P|X)\(A)Q (see p. 23). MSIA715.02