MUE: Multi User UML Editor – Suhadi Lili, Sutarsa, Siti Rochhimah
ISSN 1858-1633 2005 ICTS 43
view consistency among diagrams, because it will only shown in one diagram. For this kind of element
hierarchies, we do not apply bridge pattern [2][3].
2.3. Diagram Element
Diagram element represents the container of a glyph object. There are 8 derivation classes of
UMLDiagram as being implemented by our application. The diagram hierarchy of these 8 classes
can be seen in Figure 7.
UmlDiagram UmlAct ivit yDiagram
UmlClassDiagram UmlComponent Diagram
UmlDeployment Diagram UmlSt at eChart Diagram
UmlUseCaseDiagram UmlCollaborat ionDiagram
UmlSequenceDiagram UmlElement
Figure 10 Element Diagram Hierarchy
2.4. Editing
In our implementation, the editing process can be seen from two sides, i.e. at the client side and at the
server side. Although the client application has the direct interaction with the user actions, any editing
command on the model is not carried out by the client. The editing command, i.e. insert, update, or delete, is
passed by the client to the server. The server takes the decision whether an editing command will be
committed or not, and then notifies its decision to corresponding clients. As soon as client receives the
notification, it will update its view accordingly.
The client application consists of Diagram Editor Form and Model Explorer. The diagram editor form
provides the user with means to edit a diagram. In this form, user interacts with the glyph objects. Figure 8
shows the use cases available in diagram editor form.
autentified us er m em ilih elem en
Drag elem en res ize elem ent
hapus elem en m em buat elem en baru
Form diagram
render gam bar m em inta m em buat em en graph
m em inta m odifikasi elem en graph m em inta delete elem en
s inkronisas i data dengan s erver m enotifikas i client atas perubahan
fro m Use-Ca se M o de l
Diagram controller
f rom U s e-C as e Model
Figure 11 Use-cases for Diagram Editor Form
The model explorer displays the model element according to the hierarchy of the element, which is
viewed as a tree. In model explorer, user can interact with the model. Figure 9 shows the use cases available
in model explorer.
m enam bahkan elem en baru kondis inya dis ini adalah
aplikas i client m em inta s erver untuk m em buat
elem en
renam e elem en autentified us er
f rom ak si di f orm diagram
ubah s pes ifikas i tam pilkan s pes ifikas i
include
delete elem en pada tree Model explorer
m em inta delete elem ent m odel m em inta m odifikas i atribut
m em inta m em buat elem en m odel baru
Model Controller
f rom U s e-C as e Model
Figure 12 Use-cases for Model Explorer
2.5. Server Application Architecture
The server application is divided into two parts, i.e. Model Controller and Diagram Controller. The Model
Controller is responsible to handle any manipulation action on the model. While the Diagram Controller is
responsible to handle any manipulation action on the diagram. Therefore, there will only be one Model
Controller and a number of Diagram Controllers for a running project. When the client application passes an
editing command on a model element from user to the server, the command is handled by Model Controller.
While an editing command on a diagram is handled by Diagram Controller.
As already mentioned earlier, a model can be referred by many glyphs that view the model on
different kind of diagrams. As the consequence, any manipulation on a model element should be
synchronized through all of its corresponding glyphs. If a model element is deleted, then all of
corresponding glyphs should be deleted from all diagrams.
Since both objects, model and glyph, are handled by different Controllers, there should be a mechanism
between both controller to handle such object manipulation. In our architecture, we used an observer
pattern to represent the relation [2][3]. Figure 10 displays the implementation of this patter to these
controllers.
BaseDiagramCont roller
+ OnModelElementCreated + OnModelElementDeleted
+ OnModelElementModified
ModelCont roller
_lastUndoEnabledUserSession : long = -1 _lastUndoSequence : long = 0
UndoLength : int = 20 + CreateShapeBasedModelElement
+ CreateRelationBasedElement + StoreUndoData
+ «get» TopLevelPackage _modelController
I List eningDiagram
- _diagramControllerList 0..1
Figure 13 Class Relation: Model and Diagram Controller
Given this architecture decision, a Model Controller can immediately manage a model element
manipulation through all the Diagram Controller.
2.6. Undo
The undo command requires the application to store all previous states, model element and glyph,
that follows sequence of manipulations. When an undo command is initiated, the application not only
should reverse the sequence but also execute the opposite manipulation commands. For example, if an
Information and Communication Technology Seminar, Vol. 1 No. 1, August 2005
ISSN 1858-1633 2005 ICTS 44
undo on a delete command is initiated, the application should recreate the deleted object.
Memento Pattern
In the manipulation action, the application modifies a model element or glyph. Therefore, in the
state storing process, the internal variables of the object should be copied. These internal variables are
probably private attributes of the object. It means that it cannot be accessed from outside. If we change these
variables as public, we might intrude its encapsulation function.
To solve this problem, we introduce memento pattern [3]. The class that contains the internal
variables that need to be stored is added with a method, SaveCurrentState for model element and
SaveGraphState for glyph, that instantiate a memento class, which will store the internal variables. Figure 11
and 12 show the implementation of memento pattern.
UmlElement
+ SaveCurrentState + CopyAttributeFromStateSaver
UmlElement Mement o
«property» + SubElementState
- _UmlElementMemento 0..1
Figure 14 Memento class for Model Element
BaseGraph
+ GetGraphState + CopyAttributeFromStateSaver
GraphMement o
- _GraphMemento 0..1
Figure 15 memento class for Glyph
State Saving Mechanism
As already shown, a modification can be done on an model element or a glyph. Any modification
requires the application to save the state before the modification takes effect. Therefore, any modification
on a model element or glyph needs to be stored in a form of UndoItem or DiagramUndoItem, respectively.
UML diagrams are correlated with each other. Any modification on a model element may require
modifications on other diagrams. Therefore, it is not a wise architecture decision to implement the undo stack
on a diagram level. Because it means that each diagram save its own undo information. The
information for undo command needs to be integrated. The state of a model element that needs to be saved is
embedded into its class structure, as shown in Figure 13.
DiagramUndoI t em
+ «property» CreatedElementID : int [ ] + «property» ModifiedElementSavedState : GraphMemento [ ]
+ «property» DeletedElementSavedState : GraphMemento [ ] + «property» UndoDataOwnerID : int
UndoI t em
+ «property» UndoSequenceNumber : long + «property» UndoDataOwner : long
+ «property» CreatedModelElementID : int [ ] + «property» ModifiedElement : UmlElementMemento [ ]
+ «property» DeletedItemState : UmlElementMemento [ ]
- _DiagramUndoItem
Figure 16 Class diagram for saving states
The UndoItem can be describe as follows: UndoSequenceNumber, a sequence number of
undo information. This number is used to verify whether an undo request is correspond to the
sequence number. If it is not, than an undo request is rejected.
DataOwner, the id of a user that has the right to request the undo, that is, the user that initiates the
modification. CreatedModelElementID, a list of created element
IDs. This attribute is filled if the modification is a create model element command.
ModifiedElement, an array of UMLElementMemento instances that holds the
states of model elements. This attribute is filled if a modification command is intitated.
DeletedItemState, a state element of a deleted model element. This attribute is filled if the
modification is a deleted model element command.
The DiagramUndoItem is quite similar to UndoItem. The only difference is that
DiagramUndoItem save the state of glyphs instance of GraphMemento.
Undo Process
The undo process begins by extracting the UndoItem data that resides on the top of the stack.
According to the modification data create, delete, update, the application decides what command should
be done in order to annul the previous action. Figure 14 shows the general scheme of undo process.
hapus elem ent buat elem ent
kopikan s tate ke dalam elem en
createditem 0 deleteditem 0
m odifieditem 0
Figure 17 Undo Process: State Diagram
MUE: Multi User UML Editor – Suhadi Lili, Sutarsa, Siti Rochhimah
ISSN 1858-1633 2005 ICTS 45
2.7. Client Views Synchronization