The Software Development Life Cycle - Software Testing: Testing Across the Entire Software Development Life Cycle - page 30

building of a house, the arhchitect's blueprint is a methodology (the architect's
recommended way of building the house), and the tools are what the construc-
tion workers use to actually build the house (nail guns, circular saws, and electric
drills).
An information system methodology is a recommended way to develop an
information system. A System Development Life Cycle (SDLC) is a series of stages
within the methodology that are followed in the process of developing and revising
an information system. A stage is a segment of an SDLC that consists of certain
types of activity. Stages are usually completed in a certain sequence using software
development tools.
Developers use system design tools for data, process, and object modeling. Data
modeling tools include entity-relationship diagrams (ERDs) and data dictionaries.
Process modeling tools include data fl ow diagrams (DFDs) and use case diagrams.
Object modeling tools include class and sequence diagrams. Business processing
uses workfl ow diagrams (WFDs).
2.3 THE EVOLUTION OF SYSTEM DEVELOPMENT
LIFE CYCLES
When the fi rst business computer was installed at General Electric in 1954, the de-
velopers had no previous experiences to guide them in the right direction. They were
forced to use trial and error. Gradually, the developers compiled a list of Do's and
Don'ts to cut down on the errors and increase the likelihood that the next develop-
ment project would be more successful.
2.3.1 The Classical SDLC
The lists of Do's were the beginning of an SDLC. The first SDLC structure,
which we will call the classical SDLC , consisted of four stages—planning,
analysis, design, and implementation. Planning consisted of such things as
defining the problem to be solved or specifying the objectives of the new sys-
tem. Analysis consisted of conducting a system study for the purpose of thor-
oughly understanding the existing system. Design consisted of defining the
processes and data to be used in the new system. Implementation consisted
of preparing the software, building the data files, assembling the hardware,
and cutting over to the new system. Figure 2.1 illustrates how these stages
were intended to be taken in sequence. The term waterfall development life
cycle is used today to describe the classical SDLC because it was based on
the assumption that each stage would be executed a single time in a specific
sequence.