CONSTRUCTION TECHNOLOGY

Construction Technology

Construction Technology

Introduction

A subsystem is is a cooperating system of runtime objects that form a cohesive group. (Packages are made up of classes, not objects.) Subsystems presents a standard set of interfaces to the outside world, and all access to the objects that comprise the subsystem should be through these interfaces. 'Message Sequence Charts' (MSCs) is a trace language which in its graphical form admits a particularly intuitive representation of system runs in distributed systems while focusing on the message interchange between communicating entities and their environment. MSC is being standardised by the International Telecommunication Union (ITU). The language is used for the design of telecommunication systems. The EUT (Mauw et al.) participates in this standardisation, using the 'Algebra of communicating processes' (ACP) for the underpinning of the semantics of MSC; see . We restrict ourselves to synchronous MSCs, i.e. MSCs for which messages being sent and received always coincide. Therefore, we use the simplified version of MSC (synchronous communication only).

The diagram at left shows both the standard and ball-and-socket-style interface notations. UML also lets you put into the box a static-model diagram showing the classes that comprise the subsystem. I've found that level of detail to be unnecessary in practice, so have not shown it.

Literature review

Actors/roles are mostly uninteresting to programmers. The dependencies are valuable in determining which use case to implement first. (I often implement the use cases that have the most incoming arrows first, since other use cases depend on them.)

Learning

State diagrams share many notational elements with activity diagrams. The main difference is that state diagrams "decorate" the transitions (directed lines between states) to indicate the method call or condition that caused the transition.

Starting and Stopping. The solid circle indicates the beginning of the sequence of activities. The circle with an X represents an end of a "flow" but not the end of the entire use case. In other words, some subtask completes, but the entire use case is not yet complete. The "target" indicates that the entire use case is complete.

Subcase (Sub-Activity). The "rake" symbol indicates that the "activity" is complex enough to merit its own activity diagram. In use-case analysis, this is a "subcase"---a stand-alone activity that occurs in more than one use case but is not large enough to be a use case in its own right.

Synchronization (Fork/Join). Used either when several activities can go on in parallel or when the order in which a set of activities execute is immaterial. The heavy bar at the top is a fork. After the fork, all activities can (but are not required to) go on in parallel. Progress cannot continue past the bar on the bottom (the join) until all the activities that feed into the join complete. You can label the join with a constraint (e.g. {joinspec= (A and B) or C}) to specify the condition that allows progress to continue. If there's no constraint, AND is assumed.

Statecharts

Identifies objects that are created by activities (box with outgoing arrow) or used by activities (box ...