Requirements

Let's dive into building a simplified, in-memory version of an online UML diagram tool, similar in spirit to Lucidchart. This isn't about recreating the entire application, but rather focusing on the core model and collaborative editing features. Forget distributed databases and complex deployment; we're concentrating on robust object-oriented design, concurrency handling, and extensibility within a single process. The core challenge is to enable multiple users to concurrently edit the same diagram, ensuring data consistency and a reasonable level of responsiveness. Think Google Docs, but for UML diagrams. The focus here is on a simplified diagram representation (e.g., classes, relationships) and real-time collaboration. This means designing classes that represent diagram elements, mechanisms for tracking changes, and a way to propagate those changes to other connected users. We want to allow users to simultaneously add, delete, and modify diagram elements while maintaining data integrity. # Requirements ## Functional Requirements 1. **Diagram Creation and Persistence:** * The system should allow users to create new diagrams. * The diagram should be persisted in-memory (for this exercise). Consider a mechanism for simple file I/O if desired to simulate persistence. * Each diagram should have a unique identifier. * Each diagram should maintain a history of changes (for undo/redo functionality). 2. **Element Management:** * Support the creation of basic UML elements: Classes, Interfaces, Associations, Generalizations, and Aggregations. * Each element should have properties such as name, position, and other relevant attributes (e.g., Class attributes/methods, association labels). * Allow adding, deleting, and modifying elements within a diagram. 3. **Relationship Management:** * Establish relationships (Associations, Generalizations, Aggregations) between elements. * Relationships should have properties such as source element, target element, and optionally a label/role. 4. **Concurrent Editing:** * Support multiple users concurrently editing the same diagram. * Implement a mechanism to handle concurrent modifications and prevent data corruption (e.g., optimistic locking or conflict resolution). * Provide a way to notify connected users of changes made by others (e.g., using an Observer pattern). 5. **Undo/Redo Functionality:** * Implement undo/redo functionality to revert changes made to the diagram. The history of changes needs to be preserved to allow multiple undos and redos. 6. **Element Locking (Optional, but Highly Recommended):** * Allow a user to lock an element while they are editing it, preventing other users from making changes. This needs to be handled in a concurrent-safe manner. 7. **Change Propagation:** * As a user makes changes to a diagram or elements within a diagram, these changes must be propagated to other users who have the diagram open in near real-time. ## Non-Functional Requirements 1. **Thread Safety:** The system must be thread-safe to handle concurrent editing by multiple users without data corruption. Consider using appropriate synchronization mechanisms (locks, atomic variables, concurrent data structures) to protect shared resources. 2. **Extensibility:** The design should be extensible to support new UML elements and relationships without requiring major code changes. Consider using design patterns such as Factory and Strategy to achieve this. 3. **Modularity:** The system should be modular, with well-defined components and interfaces. This will make it easier to test, maintain, and extend the code. 4. **Testability:** The code should be designed to be easily testable. Use dependency injection and interfaces to decouple components and facilitate unit testing. 5. **Performance:** While real-time performance is not a primary focus, the system should be reasonably efficient in handling concurrent edits. Avoid unnecessary locking and optimize data structures and algorithms. 6. **Conflict Resolution:** Design a conflict resolution strategy for cases where multiple users attempt to modify the same element simultaneously. This could involve optimistic locking, last-write-wins, or a more sophisticated merging algorithm. 7. **Change History Management:** The undo/redo mechanism should be efficient and not consume excessive memory. Consider using a command pattern to represent changes as objects and efficiently manage the history. ## Core Entities 1. **Diagram:** Represents the UML diagram itself. It contains a collection of elements and relationships, and manages the history of changes. It's the root aggregate. 2. **Element:** An abstract base class for all UML elements (Class, Interface). It defines common properties such as name, position, and unique identifier. 3. **Class:** Represents a UML class, with attributes and methods. 4. **Interface:** Represents a UML interface, with methods. 5. **Relationship:** An abstract base class for all relationships between elements (Association, Generalization, Aggregation). It defines common properties such as source element, target element, and label. 6. **Association:** Represents an association between two elements. 7. **Generalization:** Represents a generalization relationship between two elements (inheritance). 8. **Aggregation:** Represents an aggregation relationship between two elements (has-a). 9. **Change:** Represents a single change made to the diagram. This is used for undo/redo functionality. Could potentially be a `Command` interface implementation. 10. **User:** Represents a user connected to the diagram. Used for locking and notifications. 11. **LockManager:** Central manager for element locks, guaranteeing concurrency safety.

Design Online UML Diagram Tool like lucidchart.

Requirements

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