1/23
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
SOEN 387 Web-based Enterprise
Application Design
Stuart Thiel
Concordia University
Department of Computer & Software Engineering
Fall, 2014
Domain Model
Outline
Domain Model
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
2/23
What are RDGs again?
3/23
I
The hold raw data from DB records
I
The provide DB interaction behaviour
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
What is Domain Logic?
I
Behaviour associated with elements specific to the
application
I
Elements that have meaning to the users of the
application
I
Not specifically programatic classes
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
What If We Want Domain Logic?
I
What if we wanted to do something?
I
What if we wanted to qualify data?
I
What if we wanted to compare things?
I
Does .compareTo() or .equals belong in RDG?
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Active Record
I
So, if we just add Domain Logic to RDGs, we get the
Active Record pattern
I
Popular with Microsoft for a long time. . . maybe still
It works, but low cohesion in those classes
I
I
I
I
Domain Logic
Raw Database Data
DB interaction behaviour
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
POJO to the Rescue
I
So why not make a POJO that represents the record in
memory
I
Keep it totally separate from the DB stuff
I
The it could hold Domain Logic and that would make
sense
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
What About RDG Database Behaviour?
8/23
I
We still need to interact with the DB
I
In exactly the same way. . .
I
But we don’t want to store the data in whatever does it
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Table Data Gateway
I
A Table Data Gateway (TDG) fits the bill
I
Abstract Class with static methods to do everything
I
Takes raw data and adjusts DB
I
Takes DB and returns raw data (RecordSets)
I
Doesn’t know or care about these POJOs
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
How to Get to the POJO?
10/23
I
So where do we get the POJO?
I
The TDG is at a lower level, POJO is clearly in Domain
I
We need something that can use the TDG as a service
to decide which POJOs to make
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Data Mapper
I
The Data Mapper fits this well!
I
It takes raw data/POJOs in finders and uses the TDG
service to get ResultSets
I
It then converts the ResultSets into one or more POJO
as needed
I
It takes the related POJOs and pulls out necessary raw
data for insert/update/delete using the TDG service
I
One Mapper per type of POJO
I
Inheritance? Think about it, but we’ll do that later.
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Diagram of POJO/TDG/DM
12/23
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
I
Splits off the database behaviour from everything else
Fowler’s Joint TDG/Data Mapper
I
Fowler Merges the Data Mapper and TDG and calls it a
Data Mapper
I
It spans two Layers. . . is that good?
I
Larman identifies that it’s easy and sensible to just split
it into the two we use.
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Diagram of Fowler’s DM
14/23
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
I
Does everything that Larman’s version does, just all in
one class
Making a Domain Model Diagram to Pick
POJOs
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
I
How do we know which POJOs to use?
I
This is the most fundamental question in your webapp
architecture
I
Talk with client, understand requirements
I
Make a Domain Model Diagram that makes sense to
them
Domain Model
Checkers Example
I
Forget Players for now, let’s talk about the game
I
We conceptually have boards
I
We conceptually have pieces
I
Are Boards first-class objects?
I
Are Pieces first-class objects
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
What Behaviours for Checkerboards/Pieces?
I
What are the behaviours in a Checkers Game
I
I
I
I
Pieces move
Pieces eat other pieces
Pieces upgrade to kings
A Player wins
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Where Does Checkerboard/Piece Behaviour
Belong?
18/23
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
I
So, should the board track winning?
I
Should the pieces track everything else?
Domain Model
Uber OO Design Diagram
19/23
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Conservative OO Design Diagram
20/23
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
What Does Checkerboard Record Store?
I
Consider the more conservative design
I
A Checkerboard record stores the location of all pieces
I
64 bits is enough to store all pieces of one type
I
There are four types of piece, king/normal for both sides
I
Can use fancy masks and store as 3 64bit bitstrings
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
What Does Checkerboard DM Do?
I
It reads the bitstrings and converts them into a more
useable array for the Checkerboard POJO
I
Array is 8x8 and stores characters, ’r’, ’R’, ’b’, ’B’, null
I
Converts any newly updated 8x8 array back into these
three bit masks
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model
Checkerboard Behaviour
I
Decide if a move is valid
I
Decide if the move is a jump
I
Decide if a move results in a kinging
I
Make the move update 8x8 array
SOEN 387
Web-based
Enterprise
Application Design
Stuart Thiel
Domain Model