Hi meghana

I can give some help on the JSD front.

Your question 2:
The main difference is that, in JSD, an Entity is defined as
something that participates in a time ordered sequence of events
(called "actions" in JSD, but events is probably a better term). JSD
Entities are therefore identified from, and modelled in terms of,
their events. In SSADM, the identification of Entities is essentially
data driven, and does not consider events.

(The recent versions of SSADM have incorporated some JSD like ideas
in the form of "Entity Life Histories", but do not go as as far as
JSD in making event sequencing the sole formal basis for entity
identification.)

In pracice, this often does not make any difference. A JSD model and
an SSADM model of the same domain will use the same entities.
However, sometimes it does make a difference. For instance, when
modelling a lending library, SSADM might identify BOOK and LOAN as
separate entities. In JSD you would only have BOOK, as the events of
lending and returning would appear as part of the lifecycle of BOOK
meaning that no seprarate LOAN entity is needed.

Your question 3.
JSD has two forms of inter-process communication, State Vector
Inspection (SVI) and Data Stream Connection (DSC). The essential
difference between them is that in SVI the transfer of information is
initiated by the reader and in DSC it is initiated by the writer.

In the case of SVI, the reader uses a "getSV" operation to get read-
only access to the inspected process' local variables (known
collectively as its "state vector"). The inspected process is not
aware of this happening (i.e., it does not have to do anything to
make its state vector available for inspection.)

In the case of DSC, the writer puts a message onto FIFO queue using
a "write" operation. The reader obtains the message by executing
a "read" on the message queue. One queue can have many writers, but
only a single reader.

-------------------------------------------------------
You may be interested our website at www.metamaxim.com. This
describes a new modelling technique that uses the essential ideas of
JSD. The approach we describe there is more powerful than JSD in a
number of respects, and is executable.

I will try and get answers to your other questions.

Regards
Ashley



--- In ITmethods@y..., "meghana_reddy2001" <meghana_reddy2001@y...>
wrote:
> hi all
>
> could any one please explain the following:
>
> 1.Yourdon's structured analysis method places a lot of emphasis on
> events, and how this effects the developemnt of dataflow diagram in
> Yourdons method.
> 2.what is the main conceptual difference between entities in SSADM
> and JSD(jackson system development).
> 3.Mechanisms of inter-process communication in JSD.
> 4.What is the dynamic modelling in SSADM,JSD,and Yourdon.
>
> thank you
> meghana