Chapter Two: Database System Concepts and Architectures
0 likes9 views
This chapter in database systems deals with Data Models and Their Categories, Schemas, Instances, and States, Three-Schema Architecture, Data Independence, DBMS Languages and Interfaces, DBMS Component Modules, Client-Server Architectures, Centralized DBMS Architecture, Distributed Database, Architecture and Cloud-based Database Architecture.
Chapter Two: Database System Concepts and Architectures
- 1. COURSE CODE : ECEg 4181 BY : EYOB S. EMAIL : eyobce@gmail.com 2
- 2. § Data Models and Their Categories § Schemas, Instances, and States § Three-Schema Architecture § Data Independence § DBMS Languages and Interfaces § DBMS Component Modules § Client-Server Architectures § Centralized DBMS Architecture § Distributed Database Architecture § Cloud-based Database Architecture 3/5/2024 ECEg 4181 - By: Eyob S. 2
- 3. §Intelligent Traffic Management System § Patient Monitoring System § Cattle Monitoring System §Smart Agriculture (farm) System 3/5/2024 ECEg 4181 - By: Eyob S. 3
- 4. nData model: a conceptual framework that defines how data is structured, organized, & manipulated nIt provides a blueprint for designing databases nIt ensures that data is stored efficiently and can be retrieved accurately nIt is essential for understanding the relationship between data and for ensuring consistency and integrity of the database nTypes of data model includes: conceptual data model, logical data model, and physical data model 3/5/2024 ECEg 4181 - By: Eyob S. 4
- 5. § Operations are used for specifying database retrievals and updates by referring to the database structure definitions (called constructs) of the data model § Constructs typically include elements (and their data types) as well as groups of elements (e.g entity, record, table), and relationships among such groups § Operations on the data model may include: § generic/basic model operations (e.g. insert, delete, update) § user-defined operations (e.g. compute_student_gpa, update_inventory) 3/5/2024 ECEg 4181 - By: Eyob S. 5
- 6. § Conceptual (high-level, semantic) data models § provide concepts that are close to the way many users perceive data (Also called entity-based, object-based data models) § Logical (representational) data models § concepts that may be understood by end users but that are not too far removed from the way data is organized within the computer § hide some details of data storage but can be implemented on a computer system in a direct way § Physical (low-level, internal) data models § concepts that describe details of how data is stored in the computer § meant for computer specialists, not for typical end users 3/5/2024 ECEg 4181 - By: Eyob S. 6
- 7. § Represents high-level concepts and relationships between data § Focuses on what data is needed and how it should be organized § Independent of any specific database management system (DBMS) § Often used in the initial stages of database design § Example: Entity-Relationship (ER) Model 3/5/2024 ECEg 4181 - By: Eyob S. 7
- 8. § Defines how the system should implement the data structure, regardless of the DBMS § Includes detailed attributes, keys, and relationships § Often used to translate the conceptual model into a more technical design § Example: Relational Model, Hierarchical Model, Network Model 3/5/2024 ECEg 4181 - By: Eyob S. 8
- 9. § Describes how data is stored in the database at the physical level § Includes details like storage structures, indexing, partitioning, and access methods § Specific to a particular DBMS (e.g., MySQL, Oracle, MongoDB) § Focuses on optimization and performance 3/5/2024 ECEg 4181 - By: Eyob S. 9
- 10. § Database Schema § A database schema is the skeleton structure that represents the logical view of the entire database § It defines how the data is organized and how the relationships among them are associated and formulates all the constraints that are to be applied on the data § Essentially, the schema is a static design—it doesn’t change as the data in the database changes. § Schema Diagram § A diagrammatic display of (some aspects of) a database schema 3/5/2024 ECEg 4181 - By: Eyob S. 10
- 11. INCOMPLETE 3/5/2024 ECEg 4181 - By: Eyob S. 11
- 12. 3/5/2024 ECEg 4181 - By: Eyob S. 12
- 13. 3/5/2024 ECEg 4181 - By: Eyob S. 13
- 14. § Database Schema § This is the structure or blueprint of a database § It defines how data is organized and how relationships among data are established § Database Instance § A database instance refers to the data stored in a database at a particular moment in time § It represents a snapshot of the database § Database schema is intension (static) § Database instance is extension (dynamic) 3/5/2024 ECEg 4181 - By: Eyob S. 14
- 15. 3/5/2024 ECEg 4181 - By: Eyob S. 15
- 16. 3/5/2024 ECEg 4181 - By: Eyob S. 16
- 17. § Database Instance § refers to the actual data stored in the database at a given moment in time § It reflects a snapshot of the database's contents, including all the tables, rows, and other data elements § The instance changes as the database undergoes operations like insertions, deletions, and updates § Database State § This is a broader term that describes the overall state of the database system, which includes its current data, the associated metadata, and its operational state. § The database state reflects the consistent and valid state of the data after transactions have been completed and committed to the database. 3/5/2024 ECEg 4181 - By: Eyob S. 17
- 18. 3/5/2024 ECEg 4181 - By: Eyob S. 18 § The word schema means arrangement – how we want to arrange things that we have to store § The diagram above shows the three different schemas used in DBMS, seen from different levels of abstraction
- 19. 3/5/2024 ECEg 4181 - By: Eyob S. 19
- 20. 3/5/2024 ECEg 4181 - By: Eyob S. 20
- 21. § Internal Schema (Physical Level) § Describes how data is physically stored on storage devices. § Includes details like file formats, indexing, and storage allocation. § Focuses on optimizing storage and retrieval. § Conceptual Schema (Logical Level) § Represents the overall structure of the database. § Defines entities, relationships, and constraints without worrying about physical storage. § Used by database administrators and developers to design the database. § External Schema (View Level) § Provides user-specific views of the database. § Ensures that users only see the data relevant to them. § Hides the complexity of the database's internal and conceptual levels. § This architecture promotes data abstraction and allows changes at one level without affecting the others 3/5/2024 ECEg 4181 - By: Eyob S. 21
- 22. § Mappings: the process of transforming requests and results between schema levels § Application programs refer to an external schema, and are mapped by the DBMS to the internal schema for execution § Data extracted from the internal DBMS level is reformatted to match the user’s external view. E.g. formatting the results of an SQL query for display in a Web page § When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independence. § The higher-level schemas themselves are unchanged. Hence, the application programs need not be changed since they refer to the external schemas, which means data independence. 3/5/2024 ECEg 4181 - By: Eyob S. 22
- 23. 3/5/2024 ECEg 4181 - By: Eyob S. 23 § Data independence is the ability to modify the schema definition in one level should not affect the definition in the next higher level § Generally, there are two categories of data independence: § Logical Data Independence § is a capacity to change the conceptual schema without having to change the external schema and their associated application programs § Physical Data Independence § is a capacity to change the internal schema without having to change the conceptual schema
- 24. § Flexibility: Allows the database to evolve without disrupting applications § Maintainability: Simplifies database maintenance and upgrades § Security: Protects sensitive data through external schemas § Efficiency: Enables performance optimization without affecting applications 3/5/2024 ECEg 4181 - By: Eyob S. 24 § Logical Independence Adding a new column (`Email`) to the `Employees` table does not affect applications that do not use this column § Physical Independence Changing the storage structure (e.g., B-tree to hash index) does not affect the logical schema or applications.
- 25. § The first step to create a database through DBMS is to specify conceptual and internal schemas for the database § Data definition language (DDL): is used by the database designers to define (external/internal) schemas for the database § View definition language (VDL): is to specify user views § Storage definition language (SDL): is to specify internal schema § Data manipulation language (DML): data sublanguages embedded in high-level languages (e.g., C++, Java) § In NoSQL DBMSs, the preceding types of languages are often not emphasized or distinctly categorized 3/5/2024 ECEg 4181 - By: Eyob S. 25
- 26. § Query Processor § interprets the requests (queries) received from end user via an application program into instructions § It also executes the user request which is received from the DML compiler or DDL Interpreter § Storage Manager (also called Database Control System) is a program that provides an interface between the data stored in the database and the queries received using the DCL. § Disk Storage contains Data Files (stores the data), Data Dictionary (governs the metadata) and Indices (provides faster retrieval of data item) 3/5/2024 ECEg 4181 - By: Eyob S. 26
- 27. 3/5/2024 ECEg 4181 - By: Eyob S. 27
- 28. § The client/server architecture was developed to deal with computer environment in which a large number of PCs, workstation, file server… § A client in this framework is typically a user machine that provides user interface capabilities and local processing § A server is a system containing both hardware and software that can provide services to the client machines 3/5/2024 ECEg 4181 - By: Eyob S. 28
- 29. 3/5/2024 ECEg 4181 - By: Eyob S. 29 § This is called logical two-tier architectures because the software components are distributed over two systems: client and server § The emergence of the Web changed the roles of client and server, leading to the three-tier architecture
- 30. 3/5/2024 ECEg 4181 - By: Eyob S. 30 Client (Presentation Layer) Application Server (Business Logic Layer) Database Server (Data Layer) § Presentation layer (E.g., GUI,Web interfaces) § Presentation layer displays information to the user § Business logic layer (E.g., Application programs) § The intermediate layer or middle layer is sometimes called the Application server or Web server § This layer handles intermediate rules and constrains before data is passed up to the user or down to the database services layer (e.g., DBMS, database server) § Three-tier architecture can enhance security § Database server only accessible through middle tier and clients cannot directly access database server § If the bottom layer is split into two layers (a web server and a database server), then it is a 4-tier architecture (possible to the n-tier)
- 31. (ON-PREMISES) 3/5/2024 ECEg 4181 - By: Eyob S. 31 § Centralized database management system architecture § This is one where all the data, the database management system, and the application are housed in a single location, typically on one server. § A centralized database is typically hosted on-premises, meaning the database and its management system are physically located within the organization's premises, often on a central server.
- 32. 3/5/2024 ECEg 4181 - By: Eyob S. 32
- 33. CHARACTERISTICS § Single Location: § The database is maintained and managed on a single server. § All data access and updates occur through this central point. § Centralized Control: § A single authority manages the database, ensuring data consistency and integrity. § Simplifies administration, backup, and recovery. § Low Redundancy: Since data is not replicated across multiple servers, redundancy is reduced. § Dependent on Network: Users access the database via a network. Any network failure can disrupt access 3/5/2024 ECEg 4181 - By: Eyob S. 33
- 34. § Advantages § Simplified Management: All data resides in one location, making administration, maintenance, and updates easier. § Data Consistency: A single copy of data reduces the risk of inconsistencies. § Cost-Effective: Requires fewer resources compared to distributed databases. § Disadvantages § Single Point of Failure: If the central server goes down, the entire system becomes inaccessible. § Scalability Issues: As user numbers and data volume grow, the system might face performance bottlenecks. § Network Dependency: Access is heavily reliant on network stability and speed. § This architecture is ideal for small to medium-sized applications where high scalability and fault tolerance are not critical. 3/5/2024 ECEg 4181 - By: Eyob S. 34
- 35. 3/5/2024 ECEg 4181 - By: Eyob S. 35 § In distributed database, data is stored across multiple locations, often on different servers or devices, but logically functions as a single database system
- 36. CHARACTERISTICS § Decentralized Storage § Data is spread across multiple sites, which can be geographically dispersed. § Data Redundancy § Data is often replicated across locations to ensure reliability. § High Fault Tolerance § Even if one server fails, others continue to operate, enhancing system resilience. § Scalability § Easy to add more servers to accommodate growth. 3/5/2024 ECEg 4181 - By: Eyob S. 36
- 37. § Advantages § Faster access for users near the data's location. § Enhanced reliability and fault tolerance. § Flexible scalability to meet increased demands. § Disadvantages § Complex management and synchronization of data. § Higher risk of data inconsistency if proper protocols aren’t in place. § Use Cases § Large-scale enterprise systems (e.g., banks, retail chains). § Systems requiring local access to data in different regions. 3/5/2024 ECEg 4181 - By: Eyob S. 37
- 38. 3/5/2024 ECEg 4181 - By: Eyob S. 38
- 39. § A cloud-based database is hosted on a cloud platform (like Azure, AWS, or Google Cloud). § Data is stored remotely and accessed over the internet. Characteristics of Cloud-Based Database Architecture include: § Centralized or Decentralized § Data can be centralized or distributed across multiple servers in the cloud. § On-Demand Resources § Storage and processing resources can scale up or down as needed. § Managed Services § Cloud providers often handle backups, maintenance, and upgrades. 3/5/2024 ECEg 4181 - By: Eyob S. 39
- 40. § Advantages § Minimal upfront hardware costs. § Highly scalable and elastic to adjust to fluctuating workloads. § Reliable backups and disaster recovery options. § Disadvantages § Reliance on a stable internet connection. § Potential concerns about data privacy and security. § Cost may increase with heavy usage. § Use Cases § Startups and businesses seeking cost-efficient scalability. § Applications requiring rapid deployment and global availability. 3/5/2024 ECEg 4181 - By: Eyob S. 40
- 41. 3/5/2024 ECEg 4181 - By: Eyob S. 41 Feature Distributed DBMS Cloud-Based DBMS Location Multiple physical sites Remote servers managed by cloud provider Data Access Local or network-based Internet-based Scalability Medium to high Highly elastic and on- demand Cost Higher infrastructure cost Pay-as-you-go model Management Complex Simplified (managed by provider)
- 42. § Data models define how data is structured and organized § Database schema is the logical structure, while database instance is the actual data § Two-tier architecture is simple and fast, while three-tier architecture is scalable and secure § Data independence ensures flexibility and maintainability in database systems § Both distributed systems and cloud-based systems architectures are ideal for handling large-scale systems § Distributed systems are often chosen for control and regional performance whereas cloud-based systems shine in flexibility, scalability, and ease of use 3/5/2024 ECEg 4181 - By: Eyob S. 42
- 43. § Why are emerging data models adapting to handle the challenges of big data and IoT? § How do the concepts of entities, attributes, and relationships vary across data models? § How does the three-schema architecture improve database abstraction and independence? § What are the differences between on-premises databases, distributed databases, and cloud databases? § What are common use cases for each database type? 3/5/2024 ECEg 4181 - By: Eyob S. 43
- 44. 3/5/2024 ECEg 4181 - By: Eyob S. 44