POS System Discussion

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POS System Discussion
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Overview

• To frame our discussion, consider
• What is the purpose of the POS system in this
  course?

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Outline

• POS System
• POS Architecture
• Issues

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Point-of-Sale System (1)

• A point-of-sale terminal is a device for
  recording sales and handling payments. The POS
  terminal captures the transaction of a customer.
  The POS system provides a link between the
  customer and the business agent (the clerk), and
  between the clerk and other business activity
  (e.g., inventory control).

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Point-of-Sale System (2)
The POS system consists of

• POS hardware
• scanner, cash drawer, display, printer,
• POS software
• software provides the interface between the POS
  hardware, the clerk and storage

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Point-of-Sale System (3)

• The clerk
• The clerks job is to operate the POS hardware
  and interact with the customer.
• The clerk is not considered part of the system,
  rather the clerk must interact with the system.

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Point-of-Sale System (4)

• System such as POS typically have a layered a
  architecture.
• A layered architecture separates the solution
  into levels. Each level tackles a certain aspect
  of the solution. Usually the communication is
  between layers.

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Architecture
Presentation
The presentation layer provides the user
interface. Think of this as the software
presenting a representation for the users
benefit thus, it must be done in a manner that
the user understands. In general, the UI provides
the communication between the user and the
software.
Domain Objects
Domain objects are objects that exists in the
problem space, the users customers world.
These are the objects that are represented in the
solution space because that are required to solve
the problem.
Service objects are solution space objects,
meaning they arent domain objects. Service
objects are introduced to facilitate the
solution. The service objects provide the
interface between the domain objects and the
storage layer.
Service Objects
The storage layer provides a way to maintain
information over long periods of time (hence the
name persisten store).
Storage
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POS Architecture (1)
U
Presentation
UPC
Quantity
Total
Domain Objects
Tendered
Balance
Enter Item
End Sale
Payment
Service Objects
The presentation layer is a thin-client. It has
little responsibility for processing. The UI
contains no code for handling application logic.
Tasks are forwarded to other layers.
Storage
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POS Architecture (2)
Presentation
Domain Objects
Sale, Payment, Clerk, Customer, Manager, Payment,
Change, Receipt
Service Objects
Storage
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POS Architecture (3)
Presentation
Domain Objects
Service Objects
DatabaseBroker, SecurityManager
Storage
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POS Architecture (4)
Presentation
Domain Objects
Service Objects
Storage
Database, FileSystem
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Issues (1)

• How do we identify the problem domain objects?
• How do we allocate responsibilities to particular
  objects/layers?
• How do we provide traceability from the
  requirements to the object model?
• Why the separation of UI from application logic?

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Issues (2)

• What guidance is there, during the design
  process, for identifying service objects?
• What are the properties of the layered
  architecture in terms of quality criteria such as
  performance, modifiability, maintainability, and
  testability?
• Does the layered architecture support distributed
  development?