Drawing and Modifying Nodes and Edges

Having defined node and edge types, the user changes to the $Draw$ mode by selecting $Draw$ in the menu Mode. Now nodes may be drawn by clicking the left button on the panel of the graph or rule editor. An edge between two nodes is created by clicking on the source first and then on the target node of the edge using the left mouse button. Edges are all directed. An edge may contain one bend. There are two possibilities to draw a bend: Firstly, the bend can be inserted when creating the edge by clicking on a place in the panel between clicking on source and target nodes.
Secondly, the bend can be created or moved being in the Move mode of the editor by grabbing the edge with the left mouse button at the center point and dragging it to the desired place in the panel. Bend points can be removed by going to the center point of an edge and selecting item Straighten in its context menu. Bends can also be removed by selecting one or more edges with bends and choosing item Straighten in the Edit menu.
Being in the Select mode, a graph object can be selected by clicking on the object. A selected object is colored in green. Selecting an object twice means deselecting it. Selected objects may be duplicated, moved, deleted, mapped or unmapped.
Being in the Move mode, a graph object can be moved by pressing the left mouse button when the cursor points to a node or an edge bend, and dragging the mouse and release it. When a node is moved, incident edges are moved accordingly. The nodes and bends can also be moved by pressing and dragging the middle mouse button. In this case, the switch to the Move mode is not necessary. Moving leads to the parallel translation of the selected objects. If an object is moved outside the current editor panel, the size of the panel will be enlarged. The scroll bars then allow to access the invisible object. The nodes or bends can also be moved by middle mouse button.

An alternative to change between edit modes is to use the context pop-up menu Edit Mode that pops up by clicking the right mouse button when the cursor placed on the background of the editor panel. Here, the user can switch between general edit modes (like Draw, Select, Move, Attributes, Map, Unmap). The selected mode is valid for the whole gramma editor.

Die setting Synchron Move Mapped Objects of the context pop-up menu Edit Mode effects the rule editor only. It allows synchronized movement of mapped node and edges of a rule with the aim to improve the readability of rules.

Here is a short description of items of menu Mode:

• Draw Mode for drawing nodes and edges.
• Select Mode for selecting nodes and edges.
• Move Mode for moving nodes and bends of the edges.
• Synchron Move Mapped Objects Synchronized movement of mapped node and edges of a rule.
• Attributes Mode for setting attributes of the nodes and edges.
• Map Mode for setting rule or match morphism mappings of the nodes and edges.
• Unmap Mode for unsetting rule or match morphism mappings of the nodes and edges.
• Image_view If this mode is set, the icons will be used to visualize the nodes of all graphs. Such icons may be set only for a node type using item Image of the pop-up menu of Node Type. A Load File dialog helps you to set the icon files. NOTE: The location directory of these icon files has to be added to the CLASSPATH environment variable.

Another context pop-up menu containing graph object specific operations is evoked by a click on the right mouse button if the cursor is over a node or the small black rectangle of an edge. The operations here (like evoking the attribute editor, Delete, Copy, Select, Map, Unmap) are valid only for the graph object the menu had been opened for. A third operations menu pops up when the current graph object is selected before evoking the menu. Figure 3 shows different context menus.

Figure 3: Context Menus for Editing Operations

Please note that some items of the pop-up menu Operations are disabled. This depends on the context of graph objects:

• Item Straighten is enabled, if the corresponding graph object is an edge, otherwise - disabled.

• Item Graph Layout / Static Position is enabled, if the corresponding graph object is a node of the host graph, otherwise - disabled. This item can be used to improve layout of the transformed graphs. In this case, the new AGG graph layout algorithm ''Evolutionary Layout of Graph Transformation Sequences'' should be in use. That means, the option perform during graph transformation of the Layouter options has to be selected. The setting Static Position allows to stop mobility of the corresponding node. The position of the node stays constant during graph evolution over time.

• Item Add Identic To Rule is enabled, if the corresponding graph object is an object of the left graph of a rule only. As result of this action, an identic object in the right graph of a rule will be created and mapped to the source object. This is possible for a NAC of a rule, too.

• Item Map is enabled, if the corresponding graph object belongs to the left graph of a rule, otherwise - disabled. You may use it to define a mapping of a rule, NAC or match morphism. The current graph object will be the source of mapping. Now, clicking on another graph object to defines the target of the mapping.

• The next four items are enabled for the type graph of a grammar only.
  • Item Multiplicity

  • Item Set Parent

  • Item Unset Parent is enabled, if the corresponding graph object already has at least one parent, otherwise - disabled.

  • Item Abstract is enabled, if the corresponding graph object is a node, otherwise - disabled.