What is Editor? Different Types of Editors

Editors :-

For any computing environment interactive text editors has an important part.

• Various types of editors are:

Fig - Types of Editors

•  Text editor should be the primary interface to the computer for all
types ( ) knowledge workers.

Overview of the editing process

•  An interactive editor is a computer program that allows a user to
create an revise a target document.

•  The document means an object such as computer programs, text,
equations tables, diagrams, photographs etc.

• The  document editing process in an interactive user computer
dialogue designed to accomplish four tasks:

1)Select the part of the target document to be viewed & manipulated.
2)Determine how to format this view online and how to display it.
3)Specify and execute operations that modify the target document.
4)Update the view appropriately.

•  Selection of the part of the document to be viewed and edited
involves first traveling through the document to locate the area of
interest.

•  Traveling implies movement of the editing context to a new
position within the text. The selection of what is to be viewed and
manipulated that is controlled by filtering.

• Filtering extracts the relevant subset of the target document at the
point of interest, such as the next screenful of text or the next
statement.

•  Formatting determines how the result of the filtering will be seen as a
visible representation on a display screen or other devices.

•  In the actual editing phase, the target document is created or altered
with a set of operations such as insert, delete, replace, move and copy.

Design of an Editor :-

•  The fundamental functions in editing are travelling, editing, viewing
and display.

•  Travelling implies movement of the editing context to a new position
within the text.

•  Viewing implies formatting the text in a manner desired by the user.

• A simple text editor' may choose to combine the viewing and display
functions.

Figure below shows the simple editor :

Fig - Editor Structure

• In editing document, the start of the area to be edited is determined by the current editing pointer maintained by the editing component.

• The traveling component of the editor actually performs the setting of the current editing and viewing pointers. It also determines the point at which the viewing and editing filters.

• The current editing pointer can be set or reset explicitly by the user with traveling commands, such as next paragraph and next screen.

• When a user issue an editing command the editing component invokes the editing filter.

• Editing component filters the document to generate a new editing buffer based on the current editing pointer as well as on the editing filter parameters.

• Filtering  may  simply  consists  of the  selection  of contiguous characters beginning at the current point.

• Current viewing pointer determined the start of the area to be viewed for viewing a document.

• Current viewing pointer can be set or reset explicitly by the user with a traveling command or implicitly by the user with a travelling command or implicitly by the system as a result of the previous editing operation.

• For a given position of the editing context, the editing and viewing filters operate on the internal form of text to prepare the forms suitable for editing viewing.

• Figure below shows the block diagram of typical editor structure.

Fig - Block Diagram Of  Editor

• When the cursor position changes, the filters operate on a new portion
of text to update the contents of the buffers.

• As editing is performed, the editing filter reflects the changes into the
internal form and update the content of the viewing buffer.

• The editing and viewing buffers are independent in some cases. They
are identical sometime as shown is Figure below:

Fig - Editing & Viewing Buffer

• The editing and viewing buffer can also partially overlap or one may
be completely contained in the other.

•  For example, the user might specify a search to the end of the
document, ,carting at a character position in the middle of the screen.

•  In the above example, an editing filter creates an editing buffer that
contains the document from the selected character of the end of the
document.

• The viewing buffer contains the part of the document that is visible
on the screen. Only the last part of which is in the editing buffer.

Screen Editors:-

• Screen editor uses the what you see is what you get principle in editor design.

• A editor displays a screenful of text at a time. The user can move the cursor over the screen, position it at the point where user desires to perform some .editing and proceed with the editing directly.

• The user has full control over the entire terminal. For example over an type exiting string which user wishes to replace . User can bring the cursor over a character to be deleted and press a delete key.

• It is possible to see the effect of an edit operation on the screen.

Line Editor :-

•  Line editor is one of the simplest type of editor which uses a
buffer to store information:

• It operates in command mode. User give the command to the
editor for any operation. Editor will respond this command.

• Buffer is in the main memory. That is set aside to store the
information which is entered from the keyboard.

Merits

1)Simple for read and write.
2) Simple in design and implementation.
3)Command and responses are interleaved.

Demerits

1 )Not user friendly.
2) Context of the text is not displayed.
3)Only single line is used for editing.

Stream Editor :-
• A stream editor views the entire text as a stream of characters. This permits edit operations to cross line boundaries.

•  Stream editor typically support character line and context orient
commands.

•  In stream editor, the current editing context indicated by the
position of text pointer. This pointer can be manipulated using
positioning.

•  Stream editor maintain multiple representations.