25 The MSC Editor

The Message Sequence Chart Editor (MSC Editor) is the graphical tool that is used to edit Message Sequence Charts (MSCs). This chapter contains a reference manual to the MSC Editor; the functionality it provides, its menus, windows and symbols. For a guide to how to use the tool, see chapter 3, Editing MSC Diagrams.

Message Sequence Charts

The MSC Editor can handle any number of Message Sequence Charts. Virtually all of the Z.120 basic MSC recommendation is supported by the MSC Editor. In addition, some concepts have been added in order to make the MSC Editor an even more powerful tool when tracing simulations; messages and timers may be assigned additional statuses that map the Z.100 recommendation and that reflect the situations that are likely to occur in a real-time system.

Message Sequence Charts Pages

Pagination of Message Sequence Charts is not supported (in opposite to SDL diagrams, see "SDL Pages" on page 1160). Instead, the MSC Editor enlarges the diagram if necessary when appending graphical objects. Each MSC is thus managed as a diagram with a virtually infinite size.

The MSC Editor Window

The MSC Editor window may be resized, moved, minimized and maximized as any other window. It contains the following components (as shown in Figure 366 on page 1302).

The Drawing Area where to perform operations on MSC objects. These operations include: selecting, moving, altering, appending and removing objects.
The Menu Bar that provides the commands that can be applied to the objects within the MSC.
The Instance Ruler that allows to view the kinds of instances, even if the instance head symbols are not currently in view.
The Symbol Menu where to select the symbols and lines to be inserted into the MSC being edited.
The Text Window where to edit the text associated to the symbols. Text may be associated with the MSC chart itself, or with any symbol or line contained in the chart.
The Status Bar which displays one line of information in the Message Area stating what a command is doing when selected from a menu.
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Figure 366 : The Message Sequence Chart Editor Window. 
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(fig)  
       
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The Drawing Area

Figure 367 : The Drawing Area.Figure legend: The picture show the upper left 
		cornerof the drawing area. 
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The drawing area is the part of the window which displays the symbols, lines and text that constitute an Message Sequence Chart. The graphical notation that is used in the MSC Editor is inherited from the Z.120 definition.

The Drawing Area Boundaries

The drawing area is delimited by its boundaries, which correspond to the size of the MSC diagram. No objects are allowed be placed outside these boundaries. The drawing area uses a light background color, while the area outside the drawing area uses a grey pattern.

The Heading Symbol

The heading symbol identifies the chart type and name. It is neither editable or movable, but its contents may be altered through the means of a command (using the Rename command, see page 1328).

An MSC may be any of the following types:
- MSC
- Sub MSC
The name of an MSC may consist of any number of characters.

The MSC Editor supports the following syntaxes for the heading symbol:

-------------------------
Case  Syntax               
-------------------------
1.    MSC <name>     
2.    SubMSC <name>  
-------------------------

The Additional Heading Symbol

The additional heading symbol is a non-Z.120 feature that is included in the MSCE for the user's convenience. It should be regarded as an extension to the heading symbol, where the following information may be entered:

A reference to an SDL diagram

A set of sub MSCs.

--------------------------------------------
Symbol      Symbol       References to Z.120  
Appearance  Name                              
--------------------------------------------
(fig)       Additional   Z.120  3             
            heading                           
--------------------------------------------

MSC Symbols and Lines

Symbols are the graphical objects that build up the contents of an MSC. Lines are the graphical objects that interconnect symbols. Lines are available in the symbol box and are thus handled as symbols.

-----------------------------------------
Symbol   Symbol       References to Z.120  
Appeara  Name                              
nce                                        
-----------------------------------------
(fig)    Text         Z.120  2.4           
(fig)    Comment      Z.120  2.3           
(fig)    Instance     Z.120  4.2           
         head                              
(fig)    Instance 

   Z.120  4.2           
         end                               
(fig)    Message      Z.120  4.3           
(fig)    Message-to-  Z.120  4.3           
         self                              
(fig)    Condition    Z.120  4.4           
(fig)    Timer(a)     Z.120  4.5           
(fig)    Action       Z.120  4.6           
(fig)    Create       Z.120  4.7           
(fig)    Stop         Z.120  4.8           
(fig)    Coregion     Z.120  5.1           
-----------------------------------------

(a): The Z.120 symbols timer set and time-out are merged into one symbol, the SDT MSCE timer symbol.

Syntax Checking on Symbols and Lines

The MSC Editor checks that the symbols are positioned in the MSC in accordance to rules governed by Z.120. Lines are always connected to at least one symbol, they are not allowed to exist on their own. The MSC Editor checks that lines are connected to symbols in accordance to Z.120.

Graphical Properties of Symbols and Lines

All symbols that are available in the symbol menu are selectable and moveable; they can be placed automatically by the tool or may, as long as the Z.120 syntax rules are respected, be assigned arbitrary locations by the user. Lines are selectable; they may be moved and reconnected by the user. Some layout work is performed automatically by the MSC Editor when drawing the line.

Most of symbols are not resizeable; these are indicated by grayed selection squares. Other symbols may be resized; this is shown by a filled selection square.

Figure 368 : Resizeable and Non-resizeable Symbol. 
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Any symbol is allowed to overlap any other symbol.

Textual Attributes

Textual objects are the textual attributes that are related to a symbol or a line. Each of these attributes is prepared by the MSC Editor - the user needs of course to fill in their textual contents.

Some MSC symbols have one or multiple text attributes. A text attribute should be filled with an MSC-PR expression (textual expression) that is syntactically correct according to Z.120, alternatively filled with some informal text if the MSC concept is used informally.

A symbol's text attributes are shown with a box when the symbol is selected

Figure 369 : A Symbol with its Text Attributes.Figure legend: The symbol (an 
		instancehead in this case) is selected and its three text attributes are shown with 
		boxes.
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Textual objects are selectable and editable. Text attributes related to messages and timers may be moved freely by the user. Textual objects are allowed to overlap any other objects.

The following textual objects are defined:

-------------------------------------
Graphical   Textual objects            
Appearance                             
-------------------------------------
(fig)       ·  Instance kind           
               Instance name           
            
   Instance decomposition  
(fig)       ·  Message name            
            
   Message parameters      
(fig)       ·  Create parameters       
(fig)       ·  Timer name              
            
   Timer parameters        
-------------------------------------

The size of the instance head and instance end symbols is 20 * 4 mm. The width / height relationship is fixed 5:1.
The text symbol, additional heading symbol and comment symbol will automatically swell or shrink to enclose the text they contain. The text and additional heading symbols may also be resized manually.
The action and condition symbol have a predefined size which cannot be altered.

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