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SCOPE OF |
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SOFTWARE
ENGINEERING |
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Historical aspects |
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Economic aspects |
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Maintenance aspects |
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Specification and design aspects |
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Team programming aspects |
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The object-oriented paradigm |
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Terminology |
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Historical Aspects |
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1968 NATO Conference, Garmisch |
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Aim: to solve the “Software Crisis” |
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Software is delivered |
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Late |
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Over budget |
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With residual faults |
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Why cannot bridge-building techniques be used to
build operating systems? |
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Attitude to collapse |
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Imperfect engineering |
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Complexity |
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Maintenance |
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Software Engineering is not “Engineering” |
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Economically viable techniques |
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Coding method CMnew is 10% faster
than currently used method CMold. Should it be used? |
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Common sense answer |
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Of course! |
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Software Engineering answer |
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Consider the effect of CMnew on
maintenance |
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Software Life Cycle |
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The way we produce software, including |
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The life-cycle model |
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The individuals |
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CASE tools |
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1. Requirements phase |
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2. Specification phase |
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3. Design phase |
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4. Implementation phase |
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5. Integration phase (in parallel with 4) |
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6. Maintenance phase |
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7. Retirement |
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1976–1981 data |
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Maintenance constitutes 67% of total cost |
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Good software is maintained—bad software is discarded |
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Different types of maintenance |
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Corrective maintenance [about 20%] |
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Enhancement |
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Perfective maintenance [about 60%] |
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Adaptive maintenance [about 20%] |
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Effect of CMnew on maintenance |
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60 to 70 percent of faults are specification and
design faults |
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Data of Kelly, Sherif, and Hops [1992] |
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1.9 faults per page of specification |
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0.9 faults per page of design |
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0.3 faults per page of code |
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Data of Bhandari et al. [1994] |
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Faults at end of the design phase of the new
version of the product |
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13% of faults from previous version of product |
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16% of faults in new specifications |
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71% of faults in new design |
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Hardware is cheap |
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We can build products that are too large to be
written by one person in the available time |
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Teams |
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Interface problems |
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Meetings |
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The structured paradigm had great successes
initially |
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It started to fail with larger products (>
50,000 LOC) |
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Maintenance problems (today, up to 80% of
effort) |
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Reason: structured methods are |
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Action oriented (finite state machines, data
flow diagrams); or |
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Data oriented (entity-relationship diagrams,
Jackson’s method); |
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But not both |
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Both data and actions are of equal importance |
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Object: |
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Software component that incorporates both data
and the actions that are performed on that data |
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Example: |
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Bank account |
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Data: account balance |
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Actions: deposit, withdraw, determine
balance |
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Information hiding |
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Responsibility-driven design |
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Impact on maintenance, development |
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Conceptual independence |
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Encapsulation |
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Physical independence |
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Information hiding |
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Impact on development |
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Physical counterpart |
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Impact on maintenance |
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Independence effects |
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Also called “Design by Contract” |
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Send flowers to your aunt in Iowa City |
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Call 1-800-FLOWERS |
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Where is 1-800-FLOWERS? |
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Which Iowa City florist does the delivery? |
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Information hiding |
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Object-oriented paradigm |
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“Send a message to a method [action] of an
object“ |
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Structured paradigm: |
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Jolt between analysis (what) and design (how) |
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Object-oriented paradigm: |
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Objects enter from very beginning |
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Systems analysis |
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Determine what has to be done |
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Design |
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Determine how to do it |
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Architectural design—determine modules |
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Detailed design—design each module |
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Object-oriented analysis |
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Determine what has to be done |
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Determine the objects |
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Object-oriented design |
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Determine how to do it |
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Design the objects |
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Do not use the object-paradigm to enhance a
product developed using the structured paradigm |
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Water and oil do not mix |
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Exception: if the new part is totally disjoint |
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Example: adding a GUI (graphical user interface) |
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Quality |
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Program, system, product |
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Methodology, paradigm |
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Method and technique |
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Client, developer, user |
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Bug ! |
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“A bug ! crept into the code” |
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instead
of |
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“I made a mistake” |
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Data component of an object |
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State variable |
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Instance variable (Java) |
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Field (C++) |
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Attribute (generic) |
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Action component of an object |
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Member function (C++) |
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Method (generic) |
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C++: A member is either an |
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Attribute (“field”), or a |
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Method (“member function”) |
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Java: A field is either an |
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Attribute (“instance variable”), or a |
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Method |
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Notes
