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Systems architecture

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A system architecture or systems architecture is the conceptual model that defines the structure, behavior, and more views of a system.

An architecture description is a formal description and representation of a system, organized in a way that supports reasoning about the structure of the system which comprises system components, the externally visible properties of those components, the relationships (e.g. the behavior) between them, and provides a plan from which products can be procured, and systems developed, that will work together to implement the overall system. The language for architecture description is called the architecture description language (ADL).

Overview

There is no universally agreed definition of which aspects constitute a system architecture, and various organizations define it in different ways, including:

  • The fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution.[1]
  • The composite of the design architectures for products and their life cycle processes.[2]
  • A representation of a system in which there is a mapping of functionality onto hardware and software components, a mapping of the software architecture onto the hardware architecture, and human interaction with these components.[3]
  • An allocated arrangement of physical elements which provides the design solution for a consumer product or life-cycle process intended to satisfy the requirements of the functional architecture and the requirements baseline.[4]
  • An architecture is the most important, pervasive, top-level, strategic inventions, decisions, and their associated rationales about the overall structure (i.e., essential elements and their relationships) and associated characteristics and behavior.[5]
  • A description of the design and contents of a computer system. If documented, it may include information such as a detailed inventory of current hardware, software and networking capabilities; a description of long-range plans and priorities for future purchases, and a plan for upgrading and/or replacing dated equipment and software.[6]
  • A formal description of a system, or a detailed plan of the system at component level to guide its implementation.[7]
  • The structure of components, their interrelationships, and the principles and guidelines governing their design and evolution over time.[8]

A system architecture can best be thought of as a set of representations of an existing (or To Be Created) system, because it is used to convey the informational content of the elements comprising a system, the relationships among those elements, and the rules governing those relationships. The architectural components and set of relationships between these components that an architecture describes may consist of hardware, software, documentation, facilities, manual procedures, or roles played by organizations or people.

A system architecture is primarily concerned with the internal interfaces among the system's components or subsystems, and the interface between the system and its external environment, especially the user. (In the specific case of computer systems, this latter, special interface, is known as the computer human interface, AKA human computer interface, or CHI; formerly called the man-machine interface.)

A system architecture can be contrasted with system architecture engineering, which is the method and discipline for effectively implementing the architecture of a system [9]:

  • It is a method because a sequence of steps is prescribed to produce or change the architecture of a system within a set of constraints.
  • It is a discipline because a body of knowledge is used to inform practitioners as to the most effective way to architect the system within a set of constraints.

History

It is important to keep in mind that the modern systems architecture did not appear out of nowhere. Systems architecture depends heavily on practices and techniques which were developed over thousands of years in many other fields most importantly being, perhaps, civil architecture.

Prior to the advent of digital computers, the electronics and other engineering disciplines used the term system as it is still commonly used today. However, with the arrival of digital computers and the development of software engineering as a separate discipline, it was often necessary to distinguish among engineered hardware artifacts, software artifacts, and the combined artifacts. A programmable hardware artifact, or computing machine, that lacks its software program is impotent; even as a software artifact, or program, is equally impotent unless it can be used to alter the sequential states of a suitable (hardware) machine. However, a hardware machine and its software program can be designed to perform an almost illimitable number of abstract and physical tasks. Within the computer and software engineering disciplines (and, often, other engineering disciplines, such as communications), then, the term system came to be defined as containing all of the elements necessary (which generally includes both hardware and software) to perform a useful function.

Consequently, within these engineering disciplines, a system generally refers to a programmable hardware machine and its included program. And a systems engineer is defined as one concerned with the complete device, both hardware and software and, more particularly, all of the interfaces of the device, including that between hardware and software, and especially between the complete device and its user (the CHI). The hardware engineer deals (more or less) exclusively with the hardware device; the software engineer deals (more or less) exclusively with the software program; and the systems engineer is responsible for seeing that the software program is capable of properly running within the hardware device, and that the system composed of the two entities is capable of properly interacting with its external environment, especially the user, and performing its intended function.

By analogy, then, a systems architecture makes use of elements of both software and hardware and is used to enable design of such a composite system. A good architecture may be viewed as a 'partitioning scheme,' or algorithm, which partitions all of the system's present and foreseeable requirements into a workable set of cleanly bounded subsystems with nothing left over. That is, it is a partitioning scheme which is exclusive, inclusive, and exhaustive. A major purpose of the partitioning is to arrange the elements in the sub systems so that there is a minimum of communications needed among them. In both software and hardware, a good sub system tends to be seen to be a meaningful "object". Moreover, a good architecture provides for an easy mapping to the user's requirements and the validation tests of the user's requirements. Ideally, a mapping also exists from every least element to every requirement and test.

A robust architecture is said to be one that exhibits an optimal degree of fault-tolerance, backward compatibility, forward compatibility, extensibility, reliability, maintainability, availability, serviceability, usability, and such other quality attributes as necessary and/or desirable.

Types of systems architectures

Several types of systems architectures (underlain by the same fundamental principles[10]) have been identified as follows[11]:

  • Collaborative Systems (such as the Internet, intelligent transportation systems, and joint air defense systems)
  • Manufacturing Systems
  • Social Systems
  • Software and Information Technology Systems
  • Strategic Systems Architecture[12]

See also

References

  1. ^ From ANSI/IEEE 1471-2000.
  2. ^ From IEEE 1220-1998 as found at their glossary.
  3. ^ From the Carnegie Mellon University's Software Engineering Institute.
  4. ^ From The Human Engineering Home Page's Glossary.
  5. ^ From OPEN Process Framework (OPF) Repository.
  6. ^ From The National Center for Education Statistics glossary.
  7. ^ TOGAF
  8. ^ TOGAF
  9. ^ The Method Framework for Engineering System Architectures, Donald Firesmith et al., 2008
  10. ^ The fundamental principles of Systems Architecture, by Boris Golden
  11. ^ The Art of Systems Architecture, Mark Maier and Eberhardt Rechtin, 2nd ed 2002
  12. ^ Choosing A Strategic Systems Architecture, by Brad Day
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