CHAPTER 4 SOFTWARE CONSTRUCTION

ACRONYMS
OMG: Object Management Group
UML: Unified Modeling Language

The term software construction refers to the detailed creation of working, meaningful software through a
combination of coding, verification, unit testing, integration testing, and debugging. The Software Construction Knowledge Area is linked to all the other KAs, most strongly to Software Design and Software Testing. This is because the software construction process itself involves significant software design and test activity. It also uses the output of design and provides one of the inputs to testing, both design and testing being the activities, not the KAs in this case. Detailed boundaries between design, construction, and testing (if any) will vary depending upon the software life cycle processes that are used in a project.

1. Software Construction Fundamentals

1.1. Minimizing Complexity

A major factor in how people convey intent to computers is the severely limited ability of people to hold complex structures and information in their working memories, especially over long periods of time. This leads to one of the strongest drivers in software construction: minimizing complexity. The need to reduce complexity applies to essentially every aspect of software construction, and is particularly critical to the process of verification and testing of software constructions. In software construction, reduced complexity is achieved through emphasizing the creation of code that is simple and readable rather than clever.

1.2. Anticipating Change
Most software will change over time, and the anticipation of change drives many aspects of software construction. Software is unavoidably part of changing external environments, and changes in those outside environments affect software in diverse ways. Anticipating change is supported by many specific techniques.

1.3. Constructing for Verification
Constructing for verification means building software in such a way that faults can be ferreted out readily by the software engineers writing the software, as well as during independent testing and operational activities. Specific techniques that support constructing for verification include following coding standards to support code reviews, unit testing, organizing code to support automated testing, and restricted use of complex or hard-to-understand language structures, among others.

1.4. Standards in Construction
Standards that directly affect construction issues include
- Communication methods (for example, standards for document formats and contents)
- Programming languages (for example, language standards for languages like Java and C++)
- Platforms (for example, programmer interface standards for operating system calls)
- Tools (for example, diagrammatic standards for notations like UML (Unified Modeling Language))

Use of external standards. Construction depends on the use of external standards for construction languages,
construction tools, technical interfaces, and interactions between Software Construction and other KAs. Standards come from numerous sources, including hardware and software interface specifications such as the Object Management Group (OMG) and international organizations such as the IEEE or ISO.
Use of internal standards. Standards may also be created on an organizational basis at the corporate level or for use on specific projects. These standards support coordination of group activities, minimizing complexity, anticipating change, and constructing for verification.

2. Managing Construction
2.1. Construction Models 
Numerous models have been created to develop software, some of which emphasize construction more than others. Some models are more linear from the construction point of view, such as the waterfall and staged-delivery life cycle models. These models treat construction as an activity which occurs only after significant prerequisite work has been completed—including detailed requirements work, extensive design work, and detailed planning. The more linear approaches tend to emphasize the activities that precede construction (requirements and design), and tend to create more distinct separations between the activities. In these models, the main emphasis of construction may be coding. Other models are more iterative, such as evolutionary prototyping, Extreme Programming, and Scrum. These approaches tend to treat construction as an activity that occurs concurrently with other software development activities, including requirements, design, and planning, or overlaps them. These approaches tend to mix design, coding, and testing activities, and they often treat the combination of activities as construction. Consequently, what is considered to be “construction”
depends to some degree on the life cycle model used.

2.2. Construction Planning
The choice of construction method is a key aspect of the construction planning activity. The choice of construction method affects the extent to which construction prerequisites are performed, the order in which they are performed, and the degree to which they are expected to be completed before construction work begins. The approach to construction affects the project’s ability to reduce complexity, anticipate change, and construct for verification. Each of these objectives may also be addressed at the process, requirements, and design levels—but they will also be influenced by the choice of construction method.
Construction planning also defines the order in which components are created and integrated, the software  quality management processes, the allocation of task assignments to specific software engineers, and the other tasks, according to the chosen method.

2.3. Construction Measurement
Numerous construction activities and artifacts can be measured, including code developed, code modified, code reused, code destroyed, code complexity, code inspection statistics, fault-fix and fault-find rates, effort, and scheduling. These measurements can be useful for purposes of managing construction, ensuring quality during construction,improving the construction process, as well as for other reasons. See the Software Engineering Process KA for more on measurements.

3. Practical considerations
Construction is an activity in which the software has to come to terms with arbitrary and chaotic real-world
constraints, and to do so exactly. Due to its proximity to real-world constraints, construction is more driven by practical considerations than some other KAs, and software engineering is perhaps most craft-like in the construction area.

3.1. Construction Design
Some projects allocate more design activity to construction; others to a phase explicitly focused on design. Regardless of the exact allocation, some detailed design work will occur at the construction level, and that design work tends to be dictated by immovable constraints imposed by the real-world problem that is being addressed by the software. Just as construction workers building a physical structure must make small-scale modifications to account for unanticipated gaps in the builder’s plans, software construction workers must make modifications on a smaller or larger scale to flesh out details of the software design during construction.
The details of the design activity at the construction level are essentially the same as described in the Software
Design KA, but they are applied on a smaller scale.


3.2 Construction Languages
Construction languages include all forms of communication by which a human can specify an
executable problem solution to a computer. The simplest type of construction language is a configuration language, in which software engineers choose from a limited set of predefined options to create new or custom software installations. The text-based configuration files used in both the Windows and Unix operating systems are examples of this, and the menu style selection lists of some program generators constitute another.
Toolkit languages are used to build applications out of toolkits (integrated sets of application-specific reusable
parts), and are more complex than configuration languages. Toolkit languages may be explicitly defined as application programming languages (for example, scripts), or may simply be implied by the set of interfaces of a toolkit. Programming languages are the most flexible type of construction languages. They also contain the least amount of information about specific application areas and development processes, and so require the most training and skill to use effectively. There are three general kinds of notation used for
programming languages, namely:
- Linguistic: Linguistic notations are distinguished in particular by the use of word-like strings of text to represent complex software constructions, and the combination of such wordlike strings into patterns that have a sentence-like syntax. Properly used, each such string should have a strong semantic connotation providing an immediate intuitive understanding of what will happen when the underlying software construction is executed.
- Formal: Formal notations rely less on intuitive, everyday meanings of words and text strings and more on definitions backed up by precise, unambiguous, and formal (or mathematical) definitions. Formal construction notations and formal methods are at the heart of most forms of system programming, where accuracy, time behavior, and testability are more important than ease of mapping into natural language. Formal constructions also use precisely defined ways of combining symbols that avoid the ambiguity of many natural language constructions.
- Visual: Visual notations rely much less on the text-oriented notations of both linguistic and formal construction, and instead rely on direct visual interpretation and placement of visual entities that represent the underlying software. Visual construction tends to be somewhat limited by the difficulty of making “complex“ statements using only movement of visual entities on a display. However, it can also be a powerful tool in cases where the primary programming task is simply to build and “adjust“ a visual interface to a program, the detailed behavior of which has been defined earlier.


3.2. Coding
The following considerations apply to the software construction coding activity:
- Techniques for creating understandable source code, including naming and source code layout
- Use of classes, enumerated types, variables, named constants, and other similar entities
- Use of control structures
- Handling of error conditions—both planned errors and exceptions (input of bad data, for example)
- Prevention of code-level security breaches (buffer overruns or array index overflows, for example)
- Resource usage via use of exclusion mechanisms and discipline in accessing serially reusable resources
(including threads or database locks)
- Source code organization (into statements, routines, classes, packages, or other structures)
- Code documentation
- Code tuning


3.3. Construction Testing
Construction involves two forms of testing, which are often performed by the software engineer who wrote the code:
- Unit testing
- Integration testing

The purpose of construction testing is to reduce the gap between the time at which faults are inserted into the code and the time those faults are detected. In some cases, construction testing is performed after code has been written. In other cases, test cases may be created before code is written. Construction testing typically involves a subset of types of testing, which are described in the Software Testing KA. For instance, construction testing does not typically include system testing, alpha testing, beta testing, stress testing, configuration testing, usability testing, or other, more specialized kinds of testing.


3.4. Reuse
As stated in the introduction of (IEEE1517-99): “Implementing software reuse entails more than creating
and using libraries of assets. It requires formalizing the practice of reuse by integrating reuse processes and
activities into the software life cycle.“ However, reuse is important enough in software construction that it is
included here as a topic. The tasks related to reuse in software construction during coding and testing are:
- The selection of the reusable units, databases, test procedures, or test data
- The evaluation of code or test reusability
- The reporting of reuse information on new code, test procedures, or test data

3.5. Construction Quality
Numerous techniques exist to ensure the quality of code as it is constructed. The primary techniques used for
construction include
- Unit testing and integration testing
- Test-first development
- Code stepping
- Use of assertions
- Debugging
- Technical reviews
- Static analysis

The specific technique or techniques selected depend on the nature of the software being constructed, as well as on the skills set of the software engineers performing the construction.
Construction quality activities are differentiated from other quality activities by their focus. Construction quality
activities focus on code and on artifacts that are closely related to code: small-scale designs—as opposed to other artifacts that are less directly connected to the code, such as requirements, high-level designs, and plans.

3.7 Integration
A key activity during construction is the integration of separately constructed routines, classes, components, and subsystems. In addition, a particular software system may need to be integrated with other software or hardware systems. Concerns related to construction integration include planning the sequence in which components will be integrated, creating scaffolding to support interim versions of the software, determining the degree of testing and quality work performed on components before they are integrated, and determining points in the project at which interim versions of the software are tested.