Visually coded applications

By : |April 13, 2006 0



By: Anadi Mishra

Tersus Studio is built on the Eclipse platform and aims
towards rapid development by modeling an application followed by defining the
semantics of the model. Tersus Modeling Language and Server are the two major
components of this platform. The modeling language defines a set of basic
components generalizing a whole genre of components usable in web applications. 



The language keeps you away from the niggles of syntactical errors as all you
have to do is choose components which would best define the model of your
application and then define a flow between the components to deliver a well knit
application model. It also includes a Visual Debugger to make things even
easier.

















Direct
Hit!
Applies to:
Developers
USP: Assemble
your application on a graphical editor 
Links: http://www.tersus.org
Google keywords:
Tersus

Modeling semantics of Tersus
Any application made
using the modeling language invariably contains the basic components viz.
Systems, Displays, Processes, Data Structures, and Data Items. System represents
a high level module and is the root of the model hierarchy. It may contain
sub-systems. It is this component that harbors multiple displays and processes.
The system can either be the full application or a major part of it.The
‘Display’ models the user interface of an application. Components such as View,
Button, Table, Tree, and Pane are all display components in the studio. Again
the language semantics allow multiple displays within a display sufficing needs
typically required by complex and interactive applications.


Processes have been modeled as ‘Actions’ by the language.
Each action is a set of activities carried out sequentially without interrupt
however the processes are synchronous in the current release. Processes can be
contained within a display and may contain lower level processes or data
elements.


Data Structure and Data Item contain information used by the
application. Data items are atomic building blocks and a data structure is
composed of lower level data structures or data items. Data structures and data
items appear in Tersus Studio as gray rectangles. 


Processes in a Tersus Application depend on flows for overall
execution. Flows govern the sequence of processes in Tersus. ‘Slots’ are
responsible for this sequential flow through processes in an application. Slots
can occur both as a ‘Trigger’ for initiating ‘Action’ in an application or as
‘Exit’ for a process. Flow appears as an arrow between two processes it is
connecting and is drawn from ‘Source’ process to the ‘Target’ process to connect
the two in a sequential link.


Elements and runtime objects 
Models in Tersus are
different from the runtime objects that are created during application
execution. Models are metadata entities — they define an application’s
functionality, but do not represent the actual details of any specific execution
of the application. Reading the models and performing actions according to the
data and conditions that prevail at runtime by the server is an indication of
this difference. In other words, a model hierarchy contains Display Models,
Process Models and Data Models and not Displays, Processes and Data Items. The
same model may be instantiated many times by the runtime engine.


The same principal applies to Models and Elements. While
model name is global i.e. it represents a reusable component and is similar to a
class definition. Elements however, represent the local name of a model element
within the model’s context.
Sample application
We will model a simple ‘Book
Store’ application using the studio. All the controls are displayed in the
‘Palette Window’ in the studio. The ‘Repository Explorer Window’ displays the
model hierarchy and the ‘Application Server’ tab displays status of applications
in the Studio. 


Designing the user interface


Our bookstore will contain two ‘Views’ — Admin and User. The
former is responsible for management tasks. Here’s how we proceed:

  • Open a new
    project from File>New>Tersus Project and name it ‘BookStore’. 

  • Double click
    on the project from the ‘Repository’ and you will find a ‘System’ component with
    a ‘View’ and a button inside the view open up. 

  • Rename the view to ‘Admin’ and
    the button to ‘Add Book’.

                                 

___________________________________________________________________________________________________________

We will now model a hierarchy wherein a popup will open up on
clicking the ‘Add Book’ button asking for the name of book while auto-generating
its ID. The values will subsequently be saved to a database and the popup
closed when the ‘Add’ button on the popup is clicked. Expand the ‘Add Book’
button by double clicking. Draw a ‘Popup’ from the ‘Display’ section into the
button, name it ‘Add New Book’ and then expand the popup Draw ‘Label’ from the
‘Display’ section of the palette into the button, followed by a ‘Text Area’.
Name the label ‘Enter Book Name’ and the text area ‘bookName’. Draw a button
named ‘Add’ in the ‘Add New Book’ popup and expand it.


Adding books to the application


Now that the user interface is complete we will model the
logic for adding books to the ‘BookStore’. 

  • Select ‘Database Record’ from the
    ‘Database’ section of palette and draw it in ‘Add’ button. We name it as ‘Book’.

  •  For representing fields of the record choose a ‘Text’ and ‘Number’ type from the
    ‘Data Types’ section and draw them in the ‘Book’ record name them ‘bookName’ and
    ‘bookID’ respectively. 

  • Draw ‘Sequence Number’ from the ‘Database’ section into
    the button and name it ‘makeBookId’ — this represents a counter for sequential
    generation of numbers. Connect this to the ‘Number’ field in the ‘Book’ record
    by drawing a ‘Flow’ from ‘makeBookId’ to ‘bookID’ thus a book id will be auto
    generated and added to the record for every new book added.






  • The complete Add New
    Book Model in the editor that allows drilling down to a specific component for
    details
  • Right click on Add button go to Add Ancestor Reference>Add
    New Book in the menu.

The Add New Book model will appear inside the ‘Add’
button. Create a flow from ‘bookName’ in the hence added ancestor to the
‘bookName’ field. This flow represents flow of data from the text area to the
‘bookName’ field in the database record of a particular book instance. 

Draw the
‘Insert Record’ component from ‘Palette/Database’ into the ‘Add’ button. Name it
‘Insert Book’ and connect flows from ‘Book’ to ‘Record ‘ slot in ‘Insert Book’.
Draw ‘Close Window’ from ‘Palette/Display Action’ into the button and connect a
flow from ‘Inserted’ slot of ‘Insert Book’ to it. Switch to ‘Application Server’
tab on the ‘Explorer’ and select ‘Book Store’, click on the green play button
with ‘1’ inscribed to start the Book Store Application only. Double Clicking the
Book Store from that view will launch the app on your browser. 

Add a few records
to see whether the model works, you will notice that the changes do not appear
until you refresh the page. To model this refreshing in Tersus we will add
another action. Zoom to ‘Add Book/Add New Book/Add’ button and draw an ‘Action’
naming it ‘Refresh Book Table’. Now simply drag the ‘Generate Book List’ action
into this action. Add a trigger to this action and connect a flow from ‘Insert
Book’ to this action to complete the modeling of this process. 

Save the project
and re-launch to see the previously added values appearing the table and auto
refreshing of the table when you add a record. This completes the modeling of
adding a new book in our application.You can similarly model Processes for
“Remove Book’ and ‘Issue Book’ tasks and request and return book tasks in an
additional ‘View’ for user.

Tracing bugs in Tersus
Tersus also provides a
visual debugging mechanism for your applications. The debugger displays errors
at design time itself where in improper flows get highlighted in red color.
Alternately errors are also displayed in a ‘Validation View’ when you are saving
a project. Tersus eases debugging by allowing you to visually trace the
execution of your application on the diagrams that have been made to create the
application.


 There is an innovative ‘Trace Mode’ provided for debugging, which
can be activated from the browser when the application is executing this records
the actions in a trace file which can subsequently be used for debugging. 


A
notable improvement in this platform in comparison to other IDE’s available is
the ability to move both backwards and forwards in execution for debugging the
application. The Studio has provided a loosely coupled framework of components for
modeling almost any real world application. It doesn’t require even a single
line of code from the developer. Moreover, you can reuse the Models and
Processes within an application to ease development efforts even further.

Source: PCQuest

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