Legacy System
A legacy system is an old system which is valuable for the company which often developed and owns it.
It is the phase __ stage of the software evolution model of Rajlich and Bennet described earlier.
Bennett used the following definition: “large software systems that we don’t know how to cope with but that are vital to our organization.”
Similarly, Brodie and Stonebraker: define a legacy system as “any information system that significantly resists modification and evolution to meet new and constantly changing business requirements.” عارف مش عارف .
There are a number of options available to manage legacy systems. Typical solution include:
______: The organization decides no further work on the legacy system should be performed.
______: An organization may decide that supporting software is not core business, and may outsource it to a specialist organization offering this service.
______: Despite all the problems of support, the organization decides to carry on maintenance for another period.
______: Throw all the software away and redevelop the application once again from scratch.
______: It is a black-box modernization technique – surrounds the legacy system with a software layer that hides the unwanted complexity of the existing data, individual programs, application systems, and interfaces with the new interfaces.
______: Legacy system migration basically moves an existing, operational system to a new platform, retaining the legacy system’s functionality and causing minimal disruption to the existing operational business environment as possible. عارف مش عارف .
Impact analysis is the task of estimating the parts of the software that can be affected if a proposed change request is made.
Impact analysis techniques can be partitioned into two classes:
__________ analysis In this approach the high-level artifacts such as requirements, design, code and test cases related to the feature to be changed are identified.
A model of inter-artifacts such that each artifact in one level links to other artifacts is constructed, which helps to locate a pieces of design, code and test cases that need to be maintained.
__________ (or __________) analysis Dependency analysis attempt to assess the affects of change on semantic dependencies between program entities. This is achieved by identifying the syntactic dependencies that may signal the presence of such semantic dependencies.
The two dependency-based impact analysis techniques are:
call ___ based analysis
and ______ graph based analysis. عارف مش عارف .
Two additional notions related to impact analysis are very common among practitioners:
_______.
_______
Ripple effect analysis measures the ______, or how likely it is that a change to a particular module may cause
problems in the ___ of the program.
Measuring ripple effect can provide ______ about the system as a whole through its ______:
-how much its ______ has increased or decreased since the previous version,
-how ______ individual parts of a system are in relation to other parts of the system, and
to look at the effect that a new module has on the complexity of a system as a whole when it is added.
The change propagation activity ensures that a change made in __ component is propagated properly
throughout the entire system.
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__________ is the process of making a change to the internal structure of software to make it easier to understand and cheaper to modify without changing its _________ behavior.
It is the object-oriented equivalent of restructuring.
Refactoring, which aims to 1-improve the ___ structure of the code, 2-achieve through the removal of duplicate code, 3-simplification, 4-making code easier to understand, 5-help to find ___ and adding flexibility to program faster.
There are two aspects of the above definition:
It must preserve the “______________” of the software system (through regression).
To improve the _____ structure of a software system (improve maintainability). عارف مش عارف .
_____________ or _____________ is
“the task of building mental models of an underlying software system at various abstraction levels, ranging from models of the __ itself to ones of the underlying application ___, for software maintenance, evolution and re-engineering purposes.”
A mental model describes a programmer’s mental representation of the program to be comprehended.
Program comprehension deals with the cognitive processes involved in constructing a mental model of the program.
A common element of such cognitive models is generating _______ and investigating whether they _______ or must be _______. Hypotheses are a way to understand code in an incremental manner. After some understanding of the code, the programmer forms a hypothesis and verifies it by reading code.
By continuously formulating new hypotheses and verifying them, the programmer understands more and more code and in increasing details.
Several strategies can be used to arrive at relevant hypotheses such as:
bottom up (starting from the code).
top down (starting from high-level goal).
opportunistic __________ of the two.
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Program Comprehension
A strategy is formulated by identifying actions to achieve a goal.
Strategies guide two mechanisms,
namely _____ and _____ to produce _____-level abstraction structures.
_______ creates new, higher level abstraction structures from lower level structures.
_______ means being able to make links elements of different abstraction levels.
Chunking and cross-referencing helps in building ________ of the program under study at different levels of abstractions. عارف مش عارف .
Software reuse was introduced by Dough McIlroy in his 1968 seminal paper:
The development of an industry of reusable source-code software components
and the industrialization of the production of application software from off-the-__ components.
Other significant early reuse research developments include:
_____________ (David Parnas).
_____________ (Jim Neighbors).
__________ are sets of programs whose common properties are so extensive that it becomes advantageous to study the common properties of these programs before analyzing individual differences.
Whereas ___________ is an activity of identifying objects and operations of a class of similar systems in a particular problem domain.
__________ is using existing artifacts or software knowledge during the construction of a new software system.
Reusable assets can be either reusable artifacts or software knowledge. عارف مش عارف .
Software Reuse
Capers Jones identified four types of reusable artifacts:
____________, involving a standardization of data formats,
______, which consists of standardizing a set of design and programming conventions dealing with the logical organization of software,
______ reuse, for some common business applications, and
____ reuse, which deals with reusing executable code.
Software reuse of previously written code is a way to 1-increase software development productivity. 2- _________ of the software.
The cost savings during maintenance as a consequence of reuse are nearly twice the corresponding savings during development.
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Reusability is a property of a software assets that indicates the degree to which it can be reused.
For software component to be reusable, it must exhibit the following characteristics that directly encourage its use is similar situation:
Environmental independence - The components can be reused irrespective of the environment from which they were originally captured.
_________ - The components that implement a single operation or set of related operations.
Loose coupling - The components that have minimal links to other components.
Adaptability - The components that are adaptable so they can be customized to fit a range of similar situation.
Understandability - The components which are easily understandable that users can quickly interpret functionality.
_________ - The components that are error-free.
Portability - The components that are not restricted in terms of the software or hardware environment they operate in. عارف مش عارف .
Benefits of Reuse
Increased reliability.
Reduced process ____.
Increase productivity.
Standards ________.
Accelerated development.
Improve _______________.
Reduction in maintenance time and effort.
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