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docs/lectures/dms/02_uml.md

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+# Unified Modelling Language
+
+12/10/20
+
+**UML**: A specification defining a graphical language for visualising, specifying, constructing and documenting the artefacts of distributed object systems.
+
+Latest version: **2.6**
+
+**Benefits of UML**
+
+- Enhances communication and ensures the right communication 
+- Captures the logical software architecture independent of the implementation language.
+- Helps to manage the complexity
+- Enables reuse of design
+
+<img src="assets/4.png" alt="img" style="zoom:80%;" />
+
+
+## Object Orientated Analysis
+
+**Use case diagrams**
+
+- Describe a set of actions that some system should or can perform in collaboration with one or more external users of the system.
+- No attempt to represent an order or a number of executions.
+
+**Use case diagram components**
+
+`Actors` - Entities that interface with the system. Can be people or other systems.
+
+`Use case` - Based on user stories and represent what the actor wants your system to do for them. In the use case diagram only the use case name is represented.
+
+`Subject` - Classifier representing a business, software system, physical system or device under analysis design, or consideration.
+
+`Relationships` 
+
+> Relationships between use case and actor
+>
+> 1. Association indicates which actor indicates which use case
+>
+> Relationship between two use cases
+>
+> 1. Specifying common functionality and simplifying use case flows
+> 2. Using <<include>>  or <<extend>>
+
+**`<<include>>`**- multiple use cases share a piece of same functionality which is placed in a separate use case.
+
+**`<<extend>>`** - Used when activities might be performed as part of another activity but are not mandatory for a use case to run successfully.
+
+
+**Use case diagram of a fleet logistics management company**
+
+![image](assets/5.png)
+
+
+**Base Path** - The optimistic path (best case scenario)
+
+**Alternative Path** - Every other possible way the system can be used/abused. Includes perfectly normal alternate use, but also errors and failures.
+
+
+Use Case: `Borrow copy of book`
+
+> **Purpose**: The book borrower (BB) borrows a book from the library using the Library Booking System (LBS)
+>
+> **Pre-conditions**: 
+>
+> 1. The book must exist
+> 2. The book must be available
+>
+> **Base Path**:
+>
+> 1. LBS requests membership card
+> 2. BB provides membership card
+> 3. BB is logged in by LBS 
+> 4. LBS checks permissions / debts 
+> 5. LBS asks for presenting a book 
+> 6. BB presents a book 
+> 7. LBS scans RFID tag inside book 
+> 8. LBS updates records accordingly 
+> 9. LBS disables anti-theft device 
+> 10. BB is logged out by LBS 
+> 11. LBS confirms that process has been completed successfully
+>
+> **Alternative Path**
+>
+> 1. BB's card has expired: Step 3a: LBS must provide a message that card has expired; LBS must exit the use case
+>
+> **Post conditions for base path**
+>
+> **Base path** - BB has successfully borrowed the book & system is up to date.
+>
+> **Alternate Path 1** - BB was NOT able to borrow the book & system is up to date.
+