View, controller, model, persistency

1
Architecture in administrative applications

• View, controller, model, persistency
• Larman chapter 30

2
Layers

• An application consists of several layers
  Larman, page 451
• Presentation layer
• GUI
• Application layer
• Controller(s)
• Domain layer
• Worker classes (alias model)
• Business layer
• We wont go into that layer in this note
• Technical layer
• Like a database layer
• Foundation layer
• Like JDBC

3
Architecture

• An architecture tells
• Which layers we need
• How to send information from one layer to another
• In this note we consider data
• Where to put data
• When to read and update date

4
Persistency

• Data must be kept on stable storage (usually hard
  disk) to prevent loss of data when the
  application stops.
• Data can be stored on the disk in
• A simple file
• A database

5
CRUD terminology

• CRUD commonly used abbreviation
• Create new data
• Read existing data
• Update existing data
• Delete existing data

6
Handling data

• Data can be handled in many ways in a layered
  application
• Memory based
• Memory based, with write through
• Like memory based
• But all CUD operation goes directly to the hard
  disk
• Other users can see the updated data
• All operations disk based
• Persistency framework

7
Memory based

• Application start
• Read data into collection classes in memory.
• Application running
• Do CRUD on the data in memory.
• Application stop
• Write the data back to the disk

8
Memory based, with write through

• Like memory based
• But all CUD operation goes directly to persistent
  store
• Other users can see the updated data immediately.

9
All operations are disk based

• Controllers does CRUD directly on the persistent
  store.
• No in-memory data.
• Domain layer not used
• Domain classes may be used for sending
  information between application and technical
  layer

10
Persistency framework

• A persistency framework moves objects from memory
  to stable storage (typically a database)
• Lots of interfaces and abstract classes in the
  technical layer.
• Reusable
• For every application
• For every type of stable storage
• Simple files
• Different DBMSes
• J2EE (Java 2 Enterprise Edition) application
  servers offers a persistency framework
• Larman, chapter 34 designs a persistency
  framework.