The document discusses the essential model and environmental model in systems analysis and design methodology. The essential model represents system requirements through abstract entities and comprises a behavioral and environmental model. The environmental model describes the system's relationships with external entities using context diagrams and an event list. A context diagram shows the system as a single process interacting with external entities. The event list catalogs all events that can trigger system output changes.

1. RTS
WARD
MELLOR
METHOD
OLOGY
BUILDING
ESSENTIAL
MODEL
ENVIRONMENTAL
MODEL

2. ESSENTIAL MODEL:-
 It is a software model, which represents the
requirements in terms of the abstract entities.
 Two parts of this model are-
1) Environmental model
2) Behavioural model
 Essential model gives ‘what’ the system is to
do.

3. ENVIRONMENTAL MODEL:-
 It mainly comprises of context diagram and
event list.
 This model describes the relationship of the
system with its environment.

4. Context Diagrams-
A context diagram is a top level (also known as
Level 0) data flow diagram. It only contains one
process node (process 0) that generalizes the
function of the entire system in relationship to
external entities
.

5.  Let us consider the example of drying oven-
Drying oven – context diagram

6. In the figure…..
 Rectangular boxes gives “terminator blocks”
which are entities exist in the environment.
 Here system is given as single bubble.
 Directed lines represent data and control
information that is passing between the system
and the environment.
Flow notations

7. Data dictionary-
In context diagram all flow should be
entered into a data dictionary, it is a part of
CASE tool. It includes following information-
 Name- the primary name of the data or control
item, or of external entity or of a process.
 Alias- other names used instead of primary
names.
 Usage- listing of processes that use it,
whether it is an input or output to a process or a
store or external entity.
 Content description- description using a
standard notation of the function.
 Other information- data types, preset values,
range of values, and other restrictions.

8. Example of data dictionary
CD- continuous data
DC- discrete control

9. Event list-
This is a table which lists all the events that
can cause a change in the system and result in
a change in an output.
Event list for drying oven
If needed we can add type of time constraint,
hard or soft, any tolerances can be indicated.

10. THANK
YOU
…