Text editors(ss)

TEXT EDITORS
Submitted by
Nishara.v
Deepthy Radhakrishnan

TEXT EDITORS
CONTENTS
 OVERVIEW OF THE EDITING PROCESS
 THE USER-INTERFACE
 EDITOR STRUCTURE

OVERVIEW OF THE EDITING PROCESS
 An interactive editor is a computer program that allows a user to create
and revise a target document. The term document includes objects such
as computer programs, texts, equations, tables, diagrams, line art and
photographs-anything that one might find on a printed page.
 The document editing process is an interactive user-computer dialogue
designed to accomplish four tasks:
1) Select the part of the target document to be viewed and manipulated
2) Determine how to format this view on-line and how to display it.
3) Specify and execute operations that modify the target document.
4) Update the view appropriately.

 Traveling – Selection of the part of the document to be viewed and edited. It involves
first traveling through the document to locate the area of interest such as “next
screenful” , ”bottom”,and “find pattern”. Traveling specifies where the area of
interest is;
 Filtering - The selection of what is to be viewed and manipulated is controlled by
filtering. Filtering extracts the relevant subset of the target document at the point of
interest such as next screenful of text or next statement.
 Formatting: Formatting determines how the result of filtering will be seen as a visible
representation (the view) on a display screen or other device.
 Editing: In the actual editing phase, the target document is created or altered with a
set of operations such as insert, delete, replace, move or copy.

THE USER-INTERFACE
 The user of an interactive editor is presented with a conceptual model of the editing
system. The model is an abstract framework on which the editor and the world on
which the operations are based.
 The line editors simulated the world of the keypunch they allowed operations on
numbered sequence of 80-character card image lines.
 The Screen-editors define a world in which a document is represented as a quarter-
plane of text lines, unbounded both down and to the right. The user sees, through a
cutout, only a rectangular subset of this plane on a multi line display terminal. The
cutout can be moved left or right, and up or down, to display other portions of the
document. The user interface is also concerned with the input devices, the output
devices, and the interaction language of the system.

INPUT DEVICES
 The input devices are used to enter elements of text being edited, to
enter commands, and to designate editable elements. Input devices
are categorized as:
1) Text devices
2) Button devices
3) Locator devices

 1) Text or string devices : They are typically typewriter like keyboards on which user
presses and release keys, sending unique code for each key. Virtually all computer key
boards are of the QWERTY type.
 2) Button or Choice devices : They generate an interrupt or set a system flag, usually
causing an invocation of an associated application program. Also special function keys
are also available on the key board. Alternatively, buttons can be simulated in software
by displaying text strings or symbols on the screen. The user chooses a string or symbol
instead of pressing a button.
 3) Locator devices: They are two-dimensional analog-to-digital converters that position
a cursor symbol on the screen by observing the user’s movement of the device. The
most common such devices are the mouse and the tablet.

 The Data Tablet is a flat, rectangular, electromagnetically sensitive panel. Either the
ballpoint pen like stylus or a puck, a small device similar to a mouse is moved over the
surface. The tablet returns to a system program the co-ordinates of the position on the
data tablet at which the stylus or puck is currently located. The program can then map
these data-tablet coordinates to screen coordinates and move the cursor to the
corresponding screen position.
 VOICE-INPUT DEVICES: which translate spoken words to their textual equivalents, may
prove to be the text input devices of the future. Voice recognizers are currently
available for command input on some systems.
 OUTPUT DEVICES The output devices let the user view the elements being edited and
the result of the editing operations.

INTERACTION LANGUAGE
 The interaction language of the text editor is generally one of several common types.
 The typing oriented or text command-oriented method It is the oldest of the major
editing interfaces. The user communicates with the editor by typing text strings both
for command names and for operands. These strings are sent to the editor and are
usually echoed to the output device.
Disadvantages:
 Have too many unique keys
 Multiple key stroke commands
 Menu oriented interface A menu is a multiple choice set of text strings or icons which
are graphical symbols that represent objects or operations. The user can perform
actions by selecting items for the menus

EDITOR STRUCTURE
 An interactive text editor has become an important part of almost any computing
environment
 Text editors act as a primary interface to the computer for all type of “knowledge
workers” as they compose, organize, study and manipulate computer-based
information.

Command Language Processor
 It accepts input from the user’s input devices, and analyzes the tokens and syntactic
structure of the commands.
 It functions much like the lexical and syntactic phases of a compiler.
 The command language processor may invoke the semantic routines directly.
 In a text editor, these semantic routines perform functions such as editing and viewing.
 The semantic routines involve traveling, editing, viewing and display functions.
 Editing operations are always specified by the user and display operations are specified
implicitly by the other three categories of operations
 Traveling and viewing operations may be invoked either explicitly by the user or
implicitly by the editing operations

Editing Component
 In editing a document, the start of the area to be edited is determined by the current
editing pointer maintained by the editing component, which is the collection of
modules dealing with editing tasks.
Traveling Component
 The traveling component of the editor actually performs the setting of the current
editing and viewing pointers, and thus determines the point at which the viewing and
/or editing filtering begins.
Viewing Component
 The start of the area to be viewed is determined by the current viewing pointer. This
pointer is maintained by the viewing component of the editor, which is a collection of
modules responsible for determining the next view.
Display Component
 It takes the idealized view from the viewing component and maps it to a physical
output device in the most efficient manner.

Editing Filter
 The editing filter filters the document to generate a new editing buffer based on the
current editing pointer as well as on the editing filter parameters
Editing Buffer
 It contains the subset of the document filtered by the editing filter based on the editing
pointer and editing filter parameters.
Viewing Filter
 When the display needs to be updated, the viewing component invokes the viewing
filter. This component filters the document to generate a new viewing buffer based on
the current viewing pointer as well as on the viewing filter parameters.
Viewing Buffer
 It contains the subset of the document filtered by the viewing filter based on the
viewing pointer and viewing filter parameters.

 There is a relationship between this classes of operations and it is considerably more
complicated than a simple model.

 Windows typically cover the entire screen or rectangular portion of it. Mapping viewing buffers to
windows that cover only part of the screen is especially useful for editors on modern graphics based
workstations. Such systems can support multiple windows, simultaneously showing different portions of
the same file or portions of different file
 This approach allows the user to perform inter-file editing operations much more effectively than with a
system only a single window.
 The mapping of the viewing buffer to a window is accomplished by two components of the system.
 (i) First, the viewing component formulates an ideal view often expressed in a device independent
intermediate representation. This view may be a very simple one consisting of a windows worth of text
arranged so that lines are not broken in the middle of words. At the other extreme, the idealized view
may be a facsimile of a page of fully formatted and typeset text with equations, tables and figures.
 (ii) Second the display component takes these idealized views from the viewing component and maps it
to a physical output device the most efficient manner possible.
 The components of the editor deal with a user document on two levels:
(i) In main memory
(ii) In the disk file system.

 Editors function in three basic types of computing environment:
(i) Time-sharing environment
(ii) Stand-alone environment
(iii) Distributed environment.
 Each type of environment imposes some constraint on the design of an editor. The Time
–Sharing Environment The time sharing editor must function swiftly within the context
of the load on the computer’s processor, central memory and I/O devices.

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