1 2 1. Introduction      The Physical Architecture Layer design models the system’s hardware, software and network environments Design for Physical Architecture Layer: [1] Reflects the non-functional requirements, e.g. operational, security and human-oriented requirements  [2] Models the infrastructure, and specifies the hardware and software of that infrastructure Most modern IT systems involve co-operating computers  Web-based systems execute in a client’s browser and interact with a Web server, and possibly kinds of other server, via the Internet  An IT system operating entirely within a company’s network may have applications on a given computer that interact with other servers, e.g. a database server, within the same network  Design for physical architecture layer must model [1] how system is distributed amongst computers, [2] the hardware of those computers and [3] the software on those computers Most systems exploit existing hardware and software infrastructure  Another significant constraint is existing hardware and software procurement arrangements, e.g. licensing and vendor agreements/relationships  Often, a variety of different infrastructures are used and hence available for “pilot” projects to evaluate new architectures and their interrelationships Effective Physical Architecture Layer design is a specialist discipline  Often, consultants (internal and/or external) are used  Non-functional requirements must be evolved into proposed architecture(s) and modelled in a UML deployment diagram  The resulting model is then used to specify the hardware and software (e.g. 3 database systems) that will support the IT system 1.1 Elements of Physical Archite