add tag sequence diagram

docs/DeveloperGuide.md

@@ -64,6 +64,14 @@ Step 2. After the user has added new travel activities into the `travelActivityL
 
 Step 3. The method will loop through each activity in `travelActivities` and add up all the expenses.
 
+### Tag feature
+
+The tag feature is implemented through the tagCommand method, which allows users to add tags to specific travel activities stored in the system.
+
+The sequence diagram depicts the interaction between the user, the tagCommand method, the TravelActivityList instance, and the OmniException instance.
+
+![TagSequenceDiagram.png](TagSequenceDiagram.png)
+
 ## Product scope
 ### Target user profile
 

docs/team/TagSequenceDiagram.puml

@@ -0,0 +1,25 @@
+@startuml
+'https://plantuml.com/sequence-diagram
+
+actor User
+
+participant "tagCommand(line: String, list: TravelActivityList)" as tagCommandMethod
+participant "list: TravelActivityList" as TravelActivityListInstance
+participant "OmniExceptionInstance: OmniException" as OmniExceptionInstance
+
+User -> tagCommandMethod: tagCommand(line, list)
+activate tagCommandMethod
+
+tagCommandMethod -> tagCommandMethod: line.split(" ")
+alt command.length == 3 && isNumeric(command[1])
+    tagCommandMethod -> tagCommandMethod: int listNumber = Integer.parseInt(command[1])
+    tagCommandMethod -> tagCommandMethod: String tag = command[2]
+    tagCommandMethod -> TravelActivityListInstance: tagActivity(listNumber, tag)
+else command.length == 2
+    tagCommandMethod -> OmniExceptionInstance: OmniException("Please specify a tag name")
+else
+    tagCommandMethod -> OmniExceptionInstance: OmniException("Please specify which task to tag")
+end
+
+deactivate tagCommandMethod
+@enduml