Introduction of Pattern Oriented Software Concepts in Ground Stations

1

• Introduction of Pattern Oriented Software
  Concepts in Ground Stations

2
Overview

• Motivation
• What are Design Patterns and Real Time Middleware
  ?
  
• ACE
• TAO
• Design Patterns
• Example The DLR GSOC Project

3
Motivation I

• Avoid to re-invent the wheel
• Problem abstraction
• Avoid making beginners faults
• Software development in a distributed and
  heterogeneous environment
  
• Cost effectiveness
• Time constraints

4
Motivation II

• Developers of distributed applications have to
  cope with inherent and accidental complexities
  
• Inherent complexity
• Eliminating race conditions"
• Deadlock avoidance
• Fault tolerance and high availability
• Load balancing
• Accidental complexity
• Lack of portable, reentrant, typesafe and
  extensible system call interfaces and component
  libraries
  
• Inadequate debugging support
• reinvention of core concepts and components

5
the result is
Middleware
Patterns
ACE
OO Design
TAO
OO Develop.
6
Bringing the pieces together

• Object oriented design allows for abstraction
• RT CORBA like ACE / TAO provides the basis for
  pattern programming
  
• Patterns are Puzzle pieces which we have to put
  together
  

7
Middleware Concepts
Satisfy specific domain requirements like Process
Automation, E-Commerce Telecommunications,
Define domain-independent services (e.g. Event
Notification, Security, )
Automate common network tasks, (e.g. Connection
and Memory Management, Synchronisation,
Multithreading, )
Encapsulate OS concurrency and IPC mechanisms
8
Overview of the ACE Framework

• Features
• Open-source
• 200,000 lines of C
• 30 person-years of effort
• Ported to Win32, UNIX, RTOSs
• e.g., VxWorks, pSoS, LynxOS, Chorus, QNX

9
Real-time CORBA TAO

• Features
• Open-source
• 500 classes 500,000 lines of C
• ACE/patterns-based
• 30 person-years of effort
• Ported to UNIX, Win32, MVS, many RT embedded
  OSs
  
• e.g., VxWorks, LynxOS, Chorus, QNX

Scheduling Service
Standard Synchronizers
Thread Pools
Protocol Properties
Explicit Binding
Portable Priorities
10
Benefits and Liabilities of Real Time CORBA
Middleware

• Cons
• Restricted efficiency due to indirection
• Multiple (distributed) points of failures
• Testing and debugging is usually more difficult

• Pros
• Patterns hide implementation and communication
• OS details are hidden as well
• Interoperability
• Reusability
• Location transparency
• Dynamic reconfiguration

11
Advantages of Real-Time CORBA Systems like ACE/TAO

• Software
• is approved
• supports timing sensitive applications
• hides the platform / OS dependent
  characteristics
  
• offers an independent abstraction layer
• used in commercial application for several years
  (e.g. military strike plane)

12
A Definition of Patterns

• "Each pattern describes a problem which occurs
  over and over again in our environment, and then
  describes the core of the solution to that
  problem, in such a way that you can use this
  solution a million times over, without ever doing
  it the same way twice
• Christopher Alexander (1977)

13
What Are Design Patterns ?

• From Douglas C. Schmidt POSA II
• Present solutions to common software problems
  arising within a certain context
  
• Help resolve key design forces
• Capture recurring structures dynamics among
  software participants to facilitate reuse of
  successful designs
  
• Generally codify expert knowledge best
  practices

14
Description of Patterns

• A pattern has four essential elements
• Pattern Name - handle
• is a handle which is used to briefly describe a
  design problem, its solutions, and consequences
  
• Problem Description - when to apply
• describes when to apply the pattern
• Solution general arrangement
• describes the elements that make up the design,
  their relationships, responsibilities, and
  collaborations
  
• Consequences - tradeoffs
• are the results and trade-offs of applying the
  pattern

15
Overview of TAO Patterns
16
Current Situation at DLR Weilheim I

• Hardware
• Old Hardware from Digital Equipment
• After Transitions Digital - Compaq HP,future
  unknown
  
• Support, maintenance
• HW upgrades
• Software
• VMS
• Fortran Code

17
GSOC Requirements

• Use of commercial of the shelf software
  components
  
• Independence of system platforms (e.G processor
  type, operating system)
  
• Support of CASE tools
• Allow for distributing the software application
• Scalability of the performance
• Allow for code reuse
• Provide application robustness

18
Current Situation at DLR Weilheim II
19
Publisher/Subscriber Pattern

• Pattern Name Publisher/Subscriber
• Problem DescriptionInformation changes in one
  place, but (potentially) many other components
  depend on this data.
  
• Solution A one-way propagation of changes is
  enabled. One component takes the role of the
  publisher and all components depending on the
  information are the subscribers. In case of a
  change, the publisher sends a notification over
  an Event Channel to the subscriber(s).
• Consequences Abstract coupling between
  publisher and subscriber Support for
  broadcast/multicast communication Risk for
  unexpected updates

20
Decoupling Suppliers Consumers
21
First Migration Step for DLR Weilheim
Future Migration Step for DLR Weilheim
22
Performance tests

• To be completedShow some estimates related to
  performance of RT CORBA Event Channels
  
• Currently we are performing test and collect
  information. Unfortunately we have not finished
  this task completely yet
  

23
Related Documentation and Web Sites

• Books
• POSA I Pattern Oriented Software Architecture
  A System of Patterns, F. Buschman et al, 1996,
  ISBN 0471958697
  
• POSA II Pattern Oriented Software Architecture
  Vol.2 Patterns for Concurrent and Networked
  Objects, 200, Douglas C. Schmidt et al, ISBN
  0471606952
• Design Patterns Elements of Reusable
  Object-Oriented Software, E. Gamma et al, 1995,
  ISBN 0201633612
  
• C Network Programming Mastering Complexity
  with ACE and Patterns, 2002, D. C. Schmidt, S.
  D. Houston, ISBN 0201604647
  
• URLs
• Pattern Homepage http//hillside.net/patterns/
• Patterns in a Nutshell http//www.enteract.com/
  bradapp/docs/patterns-nutshell.html
  
• D. Schmidts Homepage http//www.cs.wustl.edu/s
  chmidt/
  
• Riveracehttp//www.riverace.com

24
thanks for listening

• Contact
• CAM - Computer Anwendung für Management
• Rolf Kozlowski
• Rudolf-Diesel-Str. 7a
• 82205 Gilching
• Tel. [phone]
• Fax. [phone]
• Alt. Email Rolf.Kozlowski_at_ieee.org