DG: Tweak the 'Logic component' section

Main changes:
* Break the class diagram into two by extracting out the classes related
  to parsing.
* Tweak explanations to match.

docs/DeveloperGuide.md

@@ -86,27 +86,32 @@ The `UI` component,
 
 ### Logic component
 
-![Structure of the Logic Component](images/LogicClassDiagram.png)
+**API** : [`Logic.java`](https://github.com/se-edu/addressbook-level3/tree/master/src/main/java/seedu/address/logic/Logic.java)
 
-**API** :
-[`Logic.java`](https://github.com/se-edu/addressbook-level3/tree/master/src/main/java/seedu/address/logic/Logic.java)
+Here's a (partial) class diagram of the `Logic` component:
 
-1. `Logic` uses the `AddressBookParser` class to parse the user command.
-1. This results in a `Command` object which is executed by the `LogicManager`.
-1. The command execution can affect the `Model` (e.g. adding a person).
-1. The result of the command execution is encapsulated as a `CommandResult` object which is passed back to the `Ui`.
-1. In addition, the `CommandResult` object can also instruct the `Ui` to perform certain actions, such as displaying help to the user.
+<img src="images/LogicClassDiagram.png" width="550"/>
 
-Given below is the Sequence Diagram for interactions within the `Logic` component for the `execute("delete 1")` API call.
+How the `Logic` component works:
+1. When `Logic` is called upon to execute a command, it uses the `AddressBookParser` class to parse the user command.
+1. This results in a `Command` object (more precisely, an object of one of its subclasses e.g., `AddCommand`) which is executed by the `LogicManager`.
+1. The command can communicate with the `Model` when it is executed (e.g. to add a person).
+1. The result of the command execution is encapsulated as a `CommandResult` object which is returned back from `Logic`.
+
+The Sequence Diagram below illustrates the interactions within the `Logic` component for the `execute("delete 1")` API call.
 
 ![Interactions Inside the Logic Component for the `delete 1` Command](images/DeleteSequenceDiagram.png)
 
 <div markdown="span" class="alert alert-info">:information_source: **Note:** The lifeline for `DeleteCommandParser` should end at the destroy marker (X) but due to a limitation of PlantUML, the lifeline reaches the end of diagram.
 </div>
 
-### Model component
+Here are the other classes in `Logic` (omitted from the class diagram above) that are used for parsing a user command:
+
+<img src="images/ParserClasses.png" width="600"/>
 
-![Structure of the Model Component](images/ModelClassDiagram.png)
+How the parsing works:
+* When called upon to parse a user command, the `AddressBookParser` class creates an `XYZCommandParser` (`XYZ` is a placeholder for the specific command name e.g., `AddCommandParser`) which uses the other classes shown above to parse the user command and create a `XYZCommand` object (e.g., `AddCommand`) which the `AddressBookParser` returns back as a `Command` object.
+* All `XYZCommandParser` classes (e.g., `AddCommandParser`, `DeleteCommandParser`, ...) inherit from the `Parser` interface so that they can be treated similarly where possible e.g, during testing.
 
 **API** : [`Model.java`](https://github.com/se-edu/addressbook-level3/tree/master/src/main/java/seedu/address/model/Model.java)
 

docs/diagrams/LogicClassDiagram.puml

@@ -6,22 +6,11 @@ skinparam classBackgroundColor LOGIC_COLOR
 
 package Logic {
 
-package Parser {
-Interface Parser <<Interface>>
 Class AddressBookParser
-Class XYZCommandParser
-Class CliSyntax
-Class ParserUtil
-Class ArgumentMultimap
-Class ArgumentTokenizer
-Class Prefix
-}
-
-package Command {
 Class XYZCommand
 Class CommandResult
 Class "{abstract}\nCommand" as Command
-}
+
 
 Interface Logic <<Interface>>
 Class LogicManager
@@ -32,26 +21,15 @@ Class HiddenModel #FFFFFF
 }
 
 package Storage{
-Class HiddenModel #FFFFFF
 }
 
 Class HiddenOutside #FFFFFF
 HiddenOutside ..> Logic
 
-LogicManager .up.|> Logic
-LogicManager -->"1" AddressBookParser
-AddressBookParser .left.> XYZCommandParser: creates >
+LogicManager .right.|> Logic
+LogicManager -right->"1" AddressBookParser
+AddressBookParser ..> XYZCommand : creates >
 
-XYZCommandParser ..> XYZCommand : creates >
-XYZCommandParser .left.|> Parser
-XYZCommandParser ..> ArgumentMultimap
-XYZCommandParser ..> ArgumentTokenizer
-ArgumentTokenizer .left.> ArgumentMultimap
-XYZCommandParser ..> CliSyntax
-CliSyntax ..> Prefix
-XYZCommandParser ..> ParserUtil
-ParserUtil .down.> Prefix
-ArgumentTokenizer .down.> Prefix
 XYZCommand -up-|> Command
 LogicManager .left.> Command : executes >
 
@@ -64,6 +42,5 @@ note right of XYZCommand: XYZCommand = AddCommand, \nFindCommand, etc
 
 Logic ..> CommandResult
 LogicManager .down.> CommandResult
-Command .up.> CommandResult
-CommandResult -[hidden]-> Parser
+Command .up.> CommandResult : produces >
 @enduml

docs/diagrams/ParserClasses.puml

@@ -0,0 +1,38 @@
+@startuml
+!include style.puml
+skinparam arrowThickness 1.1
+skinparam arrowColor LOGIC_COLOR_T4
+skinparam classBackgroundColor LOGIC_COLOR
+
+Class "{abstract}\nCommand" as Command
+Class XYZCommand
+
+package "Parser classes"{
+Interface Parser <<Interface>>
+Class AddressBookParser
+Class XYZCommandParser
+Class CliSyntax
+Class ParserUtil
+Class ArgumentMultimap
+Class ArgumentTokenizer
+Class Prefix
+}
+
+Class HiddenOutside #FFFFFF
+HiddenOutside ..> AddressBookParser
+
+AddressBookParser .down.> XYZCommandParser: creates >
+
+XYZCommandParser ..> XYZCommand : creates >
+AddressBookParser ..> Command : returns >
+XYZCommandParser .up.|> Parser
+XYZCommandParser ..> ArgumentMultimap
+XYZCommandParser ..> ArgumentTokenizer
+ArgumentTokenizer .left.> ArgumentMultimap
+XYZCommandParser ..> CliSyntax
+CliSyntax ..> Prefix
+XYZCommandParser ..> ParserUtil
+ParserUtil .down.> Prefix
+ArgumentTokenizer .down.> Prefix
+XYZCommand -up-|> Command
+@enduml