Smalltalk and Object Orientation: an Introduction - Free

edisplay()
Controller
window
A
Window
P
(window)
1: displayPositions(window)
1.1.3.1: add(self)
wire
A
A
new contents
1.1 *(1=n): drawSegment(i)
(self)
S
Wire
1.1.2: create(r0,r1)
1.1.3: display(window)
temp (line)
A
*
new Line
1.1.1a: r0 := position()
1.1.1b: r1 := position()
A
Bead
A
Bead
Figure 18.3: An example collaboration diagram
Objects which are created during the collaboration are indicated by the label new before the obje ct
name. For example the Line object in Figure 18.3. Links between objects are annotated to indicate their
type (e.g. permanent or temporary existing for this particular collaboration). These adornments are
placed in boxes on the ends of the links and can have the following values:
A - association (or permanent) link
F - Object field (the target object is part of the source object)
G - global variable
L - local variable
P - Procedure parameter
S - self reference
Role names can also be added to distinguish links (e.g. self, wire and window in Figure 18.3). Role
names in brackets indicate a temporary link, i.e. one that is not an association.
The messages which are sent along links are indicated by labels next to the links. One or more
messages can be sent along a link in either or both directions. The format of the messages is defined by
the following (some of which are optional):
1. A comma-separated list of sequence numbers in brackets: [seqno, seqno]. The sequence numbers
indicate messages from other threads of control that must occur before the current message can
occur. This element is only needed with concurrency.
2. A sequence number containing a list of sequence elements separated by full stops (periods).
These represent the nested procedural calling sequence of the message in the overall transaction.
Each element section has the following parts:
• A letter (or name) indicating a concurrent thread. All letters at the same level of nest ing
represent threads that execute concurrently e.g. 1.2a and 1.2b are concurrent. Omitting the
letter entirely is equivalent to another dummy letter and usually indicates the main
sequence.
• An integer number. The numbers show the sequential position of th e current message
within its thread. For example, message 2.1.4 is part of the procedure invoked by message
2.1 and follows message 2.1.3 within that procedure.
• An iteration indicator. This is a star (*), optionally followed by an iteration expression in
parentheses. Iteration indicates that several messages of the same form are sent either
sequentially (to a single target) or concurrently (to the elements of a set). If there is an
iteration expression, it shows the values that the iterator or iterators assume, such as
“(i=1..n)”; otherwise the details of the iteration must be specified in text or simply deferred
to the code.
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