SOFTWARE REUSE 28 March 2013 William W. McMillan

What is the most common form of software reuse in Java programming?

Benefits of Reuse  Save resources.  Standardize a solution that can be trusted.  Support levels-of-abstraction approach to creating systems.  Encapsulated “black-box” components.  Reduce tedium, allow developers to work on new things.

Risks of Reuse  Propagate inefficient solution.  e.g., O(N 2 ) sorting routine  Propagate incorrect solution.  Stats formula could be wrong or inappropriate.  Shield developers from fundamental knowledge of how something works.  May not know inefficiencies of solution in particular context.  May miss interactions and dependencies.

Risks of Reuse  Hard to change or update reused component.  Long-term cost if there’s a license fee.  Loss of support if provider goes belly-up.

Suppose a method to compute a standard error of the mean is incorrect. What are some potential costs if the routine is used repeatedly?

History of Reuse  Copy someone’s source code to do a task.  Subroutines:  Well-defined modules, with name,  … but might use common data structures.  Call subroutines with parameters.  “Include” files.  External libraries of useful routines.  E.g., LINPACK for linear algebra and related.  Database tools like Ingres

History of Reuse  Computer simulation led to object-oriented design.  Simula 67  Packages and “Units” appeared.  UCSD Pascal, Ada.  Abstract data types influential in computer science.  Object-oriented goes mainstream:  C++, O-O capabilities bolted onto C.  Smalltalk from a more AI perspective.

History of Reuse  Java cleans up a lot of O-O trash:  Multiple inheritance gone.  No “friend” access.  Better dynamic memory management.  C# is Microsoft’s version of Java.  Packages, APIs, components now common.  A lot of development is done on top of:  Statistics packages  SQL engines  Enterprise mega-packages like SAP

How have people employed books and tutorials on programming and scripting in software reuse?

Reuse of Software Ideas  Algorithms and data structures.  Useful architectures and design patterns (discussed earlier in course).  E.g., model-view-controller  Programming styles.  Elements of Programming Style by Kernighan and Plauger  Relational databases.

What benefits do you gain in being familiar with the idea of a sparse matrix?

Software Frameworks  Integrated sets of tools and utilities.  E.g.,.NET, Enterprise Java Beans, Allegro Common Lisp.  User interface objects and methods.  Communication facilities.  Security tools.  Data structures.  Database management.  Web applications.  Session and transaction management.

What facilities do you rely on most in a software framework you use?

Families of Software Products  E.g., Microsoft Office, Adobe Creative Suite.  Might have unique scripting language.  UI has similar feel and style across members.  Compatible parts.  Common architecture.  Common data formats.  Incentives to use all or none.  Reasons to keep all parts up to date.

Do Oracle software products constitute a family?

Buy Commercial Software?  E.g., SAP, E-Commerce tools.  Why reinvent the wheel?  Why not get expert advice and help?  Reduce costs, especially maintenance.  Reduce liability.  Get things you might not have thought of:  Encryption, back-up facilities, slick algorithms,…

Use Open-Source Software?  Talk about saving costs….  But do you always save?  Where does support come from?  “Read the source code” isn’t always the help you need.  Need to consider long-term costs and risks.

When would you advise a client to consider including open-source software in a system?

Use Cloud-Based Services?  E.g., Amazon, AT&T.  Third-party provider.  Data and functions on servers managed by provider.  Includes many tools.  Access via the Internet.

A client says, “I want this to be a cloud- based system.” What questions would you ask in order to respond intelligently?