Connie's Convenience Store - About Peter Coad

Applying Patterns: Select and Organize Problem-Domain Objects Connie’s Convenience Store 21
object methods continue that tradition; that’s not enough. Here, you are working with
objects. For each object, you consider “what I know; who I know; what I do.” The first
is represented by attributes; the second is represented by object connections; the third is
represented by services. Constraints on “who I know” belong next to the object being
constrained. That’s the convention used here. It better supports “object think.”
By placing the constraint next to the object being constrained, each object’s responsibilities
for “who I know” comes through much more clearly.
#73. “Show Who I Know” Strategy establishing responsibilities /
who I know (fundamentals)
• Show “who I know” graphically, with an object connection.
Include constraints, placed next to each object being constrained: 1 0-1 n 1-n
ordered n [XOR A] 1 [OR B] 2 [C] ordered n all
“n” is the same thing as “0-n” (it’s just easier to write it as “n”).
A constraint indicates that an object has no need to know the other objects
(this may occur, notably for a part in an aggregate).
ordered n an ordered collection of some number of connections
[XOR A] 1 indicates an exclusive or, pertaining to all object connections labeled
with the same tag (in this example the tag is “A”). Place whatever constraint
applies to the right of the brackets, e.g., [XOR A] 1.
[OR B] 2 two connections, selected from the connections labeled “B”.
[C] ordered n an ordered collection of some number of connections (any connection
from that object that is labeled “C”).
• Or show “who I know” textually, with an attribute.
Use this format whenever an object connection spans across model components — or
any other time that an object connection would be cumbersome, visually.
For a textual representation, use this format:
“”
Make it singular or plural, reflecting the number of objects that the object may
know.
Another example: a cashier object knows about its corresponding session object
(the current one), as well as some number of session objects (one for each and every
time the cashier logs onto the system). This is a common situation in life: “I know
many, yet one is most important to me right now.” What can you do about it? Use both a
“current session” attribute and a cashier-session object connection.
Place-transaction
A store is a place where a sale happens. It’s an instance of place-transaction.