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Which of the following describes a foreign key in relational databases?

  • It must refer to a value present in another table. (correct)
  • It is used to combine multiple tables into one.
  • It can automatically generate values for new entries.
  • It requires values to be unique within a table.

    • What is a primary key in a relational database?

  • A unique identifier for each record in a table. (correct)
  • A key that allows deletion of records in the same table.
  • A key that links to another table for data retrieval.
  • A field that can contain multiple values.

    • Which of the following is a benefit of data independence in relational databases?

  • It separates application logic from physical data organization. (correct)
  • It requires users to understand the database system.
  • It mandates that data is stored in a single table.
  • It allows direct access to the physical storage format.

    • What is one of the main advantages of having a database administrator (DBA)?

    <p>They centralize control over database design and performance.</p> Signup and view all the answers

    What does data integrity ensure in a relational database?

    <p>Duplicate rows are prevented in the database.</p> Signup and view all the answers

    Which of the following is a disadvantage of relational databases?

    <p>They can become large and complex, requiring significant maintenance.</p> Signup and view all the answers

    What component is essential for ensuring data security in a relational database?

    <p>User permissions and access controls.</p> Signup and view all the answers

    Which task is typically performed by the database server in a relational database?

    <p>Logging user interactions and database actions.</p> Signup and view all the answers

    What does the query 'MATCH (s:Student)-[:FOLLOWING]->(c:Course) WHERE c.name = "MSc Software Development" RETURN s.name' retrieve?

    <p>The names of students enrolled in a specific course</p> Signup and view all the answers

    Which feature of MongoDB allows for flexible document structures with no enforced schema by default?

    <p>Document flexibility</p> Signup and view all the answers

    In the context of the CAP theorem, what does 'Consistency' ensure?

    <p>Every read receives the most recent write or an error.</p> Signup and view all the answers

    What is one key benefit of using graph databases in applications?

    <p>Ability to easily perform complex queries about relationships</p> Signup and view all the answers

    What language is MongoDB primarily interfaced with?

    <p>JavaScript</p> Signup and view all the answers

    Which statement accurately describes MongoDB's document structure?

    <p>Documents can vary in structure but are usually key-value pairs.</p> Signup and view all the answers

    Which of the following best describes the role of the aggregation pipeline in MongoDB?

    <p>A process similar to MapReduce for processing and transforming data.</p> Signup and view all the answers

    What is a notable difference between relational databases and NoSQL databases regarding data handling?

    <p>NoSQL databases can quickly adapt to changes in data structure.</p> Signup and view all the answers

    Which of the following statements about a relation (table) is correct?

    <p>Each tuple in a relation must be distinct.</p> Signup and view all the answers

    What best describes a schema in the context of relational databases?

    <p>A set of rules defining how data is stored and organized</p> Signup and view all the answers

    In a relational model, what is the cardinality?

    <p>The number of tuples (rows) in a relation</p> Signup and view all the answers

    What is a foreign key used for in a relational database?

    <p>To refer to primary key values from other tables</p> Signup and view all the answers

    Which statement is true about attributes in a relation?

    <p>Each attribute must have a distinct name within a table</p> Signup and view all the answers

    Which characteristic about relational databases is incorrect?

    <p>They allow the order of tuples to affect data retrieval.</p> Signup and view all the answers

    What does the term 'tuple' refer to in a relational database?

    <p>A single row of data in a table</p> Signup and view all the answers

    What is a potential application of data processing from mobile phone data?

    <p>Finding criminals</p> Signup and view all the answers

    What are schema constraints primarily used for?

    <p>To enhance critical application reliability</p> Signup and view all the answers

    Which of the following describes a distributed database?

    <p>A system with multiple servers allowing for parallel reads</p> Signup and view all the answers

    What challenge is associated with processing large volumes of data?

    <p>Processing bottlenecks</p> Signup and view all the answers

    In terms of data storage, what is one advantage of using cloud solutions?

    <p>Enhanced disaster recovery capabilities</p> Signup and view all the answers

    Which of the following is NOT a source of data mentioned?

    <p>Statistical analysis results</p> Signup and view all the answers

    What is a key requirement for a robust database server?

    <p>Ability to handle simultaneous requests</p> Signup and view all the answers

    What does the term 'resilient to failure' refer to in data processing?

    <p>The capacity to recover quickly from failures</p> Signup and view all the answers

    What is a characteristic of NoSQL databases compared to traditional SQL databases?

    <p>They use a flexible schema definition.</p> Signup and view all the answers

    Which of the following data serialization formats is used internally by MongoDB?

    <p>BSON</p> Signup and view all the answers

    Which type of NoSQL database is optimized for queries across linked entities?

    <p>Graph database</p> Signup and view all the answers

    Which of the following formats is known for minimal markup in data formatting?

    <p>YAML</p> Signup and view all the answers

    What advantage do NoSQL databases have concerning scalability?

    <p>Easier distribution of database.</p> Signup and view all the answers

    In NoSQL document stores, how is data typically organized?

    <p>As serialized documents.</p> Signup and view all the answers

    Which of the following is NOT a type of NoSQL database mentioned?

    <p>Row-oriented database</p> Signup and view all the answers

    What is a key benefit of using object-oriented programming in NoSQL object stores?

    <p>They serialize and deserialize objects automatically.</p> Signup and view all the answers

    Study Notes

    Data and Serialisation

    • The module assumes basic Python knowledge.
    • The cohort has varying abilities and experience.
    • Students should contribute to class discussions and support each other, except during exams.
    • Raise questions quickly, as confusing issues might also confuse others.
    • Test knowledge via lab exercises and revision quizzes.
    • Utilise discussion forums effectively.
    • Resources include lectures, lab sessions, programming examples, and supporting reading material. Experimentation is needed to understand concepts.
    • Assessment is individual and collaboration is prohibited.
    • The exam date is yet to be determined.
    • The exam is 50% of the grade for CS982 and 100% for CS988.
    • Revision quizzes and previous exam papers should be reviewed to prepare for the exam.
    • The exam will be a closed-book exam in the exam hall.

    Data Processing

    • Data sources include distributed sensors (wind turbines, power grid, rail network, infrastructure, white goods, mobile phones, CCTV cameras, internet documents, and social media uploads).
    • Frequent sampling leads to large datasets.
    • Possible applications include preempting maintenance, traffic modelling, finding criminals, face recognition, analysing behaviour, recommending products and services.

    Challenges

    • Large volumes of data.
    • Many different data formats.
    • Rapid analysis.
    • Distributed data analysis.
    • Processing bottlenecks.
    • Processing data in parallel.
    • Data resilience to failure.

    Considerations

    • Size of the data sample.
    • Data type (sensitive or replaceable).
    • Existing infrastructure (cluster or database server).
    • Speed or performance requirements.
    • Scalability.

    Storage Approaches

    • Database server: A single computer hosting a database and accepting connections. Can be overwhelmed by requests, but is robust.
    • Distributed database: Parallel read and single or parallel write. Many servers or database files (e.g., SQLite). Distributed files containing serialized information. Minimises bottlenecks. Can be implemented in the cloud or on-premises.

    Schema Constraints vs Evolution

    • Schema describes data structure.
    • Data may evolve or remain similar.
    • Schema constraints are more or less helpful depending on the application's needs.
    • Critical applications often need more constraints.
    • Tolerating schema changes between data records is acceptable for some applications.

    Serialisation Approaches

    • Relational databases/tables: Data stored across one or more tables. Data must match table definitions.
    • Object-based storage:
      • Uses JavaScript Object Notation (JSON).
      • Allows custom binary serialisation.
      • Can enforce or allow schema evolution

    Relational Model

    • Describes data as relations.
    • Defines high-level operations, users do not need to know the implementation.
    • No physical pointers.
    • Different database servers may use different implementations (SQL).

    Relational Databases

    • Hold data in tables (relations).
    • Example tables shown in figures.
    • Relation (table): Rows (tuples) and columns (attributes).
    • Cardinality, key, degree, and domain are aspects of relations (tables).
    • Schema: Table names, attributes, and type definitions; database schema consists of several relations and constraint names applying to tables.
    • Properties of a relation include: unique name, distinct tuples, order is irrelevant, and atomic values per field with a matching attribute type.

    Keys

    • Comprises one or more attributes used for identifying tuples (rows).
    • Primary keys: Required to be unique, can be automatically incremented.
    • Foreign keys: Refers to other tables, primary key value from other table, used to create constraints between tables.

    Relational schema constraints

    • Field type: Integer, floating point, text, etc.
    • Field length: Limits maximum value or length of text.
    • Unique values: Primary keys are unique and use auto-increment. Other unique values can use numbers or text.
    • Foreign keys: Required values in other tables prevent deletion, can cascade deletion. Schema constraints restrict data values (e.g., bank accounts, personal information).

    Relational databases benefits

    • Data Independence: Not tightly coupled to underlying implementation, does not need the physical storage format. Applications access through SQL, same logic retrieving few or many fields.
    • Data Security: Database server with user/password (TLS/SSL), permissions for access to tables/views.
    • Integrity: Prevents duplicate rows and enforces constraints. Efficient for concurrent access where transactions do not interfere with each other, resources can be scaled to meet access needs.
    • Analytics and Administration: Server logs actions, table/index size, operations, query times, and database size. Database administrator (DBA) controls design, usage, and performance tweaks.

    Relational databases disadvantages

    • The system is complex and needs maintenance.
    • Server and the database can increase considerably in size.
    • Hardware costs are needed for enhanced performance.
    • Scaling to database schema/new schema is expensive.
    • Avoid parallel write to a distributed database.

    NoSQL Approaches

    • Not only SQL (NoSQL).
    • Uses different commands compared to SQL..
    • Some inspiration from SQL (SQL - read, write and queries).
    • Typically data is not stored in tables.
    • NoSQL Types:
      • Document databases (JSON, BSON) - example MongoDB
      • Key-value pair storage - example Couchbase
      • Column-oriented databases - example Cassandra
      • Graph databases - example Neo4j

    NoSQL: Features

    • Flexible schema definition—allows differing records/documents.
    • Schema definition possible, but limited.
    • No foreign keys.
    • Easier to distribute the database and scale to address loading.
    • Data structure similar to hash tables.
    • Use of cheap storage instead of special servers

    NoSQL Types: Document Stores

    • Stored as key (text) and document; similar to key-value store.
    • Documents encompass serialized data (JSON, XML, BSON).
    • Other data serialization methods.
    • Schema constraints possible within document schema.
    • Index definition for collections.

    NoSQL Types: Object Stores

    • Key-value pair storage. Driven by object-oriented programming.
    • Serialization and deserialization of objects to/from NoSQL database,.
    • Serialized data stored as text.
    • Intuitive access.
    • Implemented in C++ or Java.
    • ACID (atomicity, consistency, isolation, durability) compliance.

    NoSQL Types: Graph Databases

    • Each data unit (node/entity) has pointers (relationships) to other entities.
    • . A graph of linked entities.
    • Optimized querying across links, faster than equivalent SQL queries.
    • Examples of fast link processing applications include shortest-path calculations and network/electricity analysis.

    MongoDB

    • MongoDB (humongous) is a document-based database using a JSON interface and BSON storage.
    • Schema definition is possible
    • Implemented in C++, JavaScript, and Python.
    • Several server types, including cloud instances and community editions.

    MongoDB: Features

    • Flexible schema.
    • Fast creation and updates.
    • Server-side JavaScript execution.
    • Flexible horizontal scaling—sharding.
    • Indexing—for rapid searches.
    • Aggregation using a pipeline similar to MapReduce.

    CAP Theorem

    • Choose a mix of properties based on the application.
    • Relational databases: Ensure ACID compliance (Atomicity, Consistency, Isolation, Durability).
    • NoSQL: Trade-offs between:
      • Consistency: Every read gets the latest write or error.
      • Availability: Every request gets a response (not necessarily the latest write).
      • Partition tolerance: System operates despite network message drops.
    • Distributed systems can fail due to temporary network partitioning.
    • Choose between consistency and availability.

    Polyglot Persistence

    • Use different data storage technologies together to leverage each's strengths.
    • Example: Relational DB for sensitive data, NoSQL for changeable data.
    • Use microservices per data type to combine in one application.

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