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neurologyYou need to know

• Lossless compression reduces file size while allowing the original data to be reconstructed exactly, whereas lossy compression permanently removes data to achieve greater compression and is suitable when some loss of quality is acceptable.
• Run-length encoding stores repeated consecutive data as a value and a count, while dictionary coding replaces repeated patterns with shorter references to entries in a shared dictionary.
• Symmetric encryption uses the same secret key for encryption and decryption, whereas asymmetric encryption uses a mathematically related public key and private key, allowing secure communication without first sharing a secret key.
• A hash function converts input data into a fixed-length hash value; hashes are used to check data integrity, index data, store passwords securely with salting, and support digital signatures, but hashing is not reversible encryption.
• A flat-file database stores data in a single table or file, whereas a relational database stores data in linked tables to reduce duplication and represent relationships between entities.
• A primary key uniquely identifies each record, a foreign key refers to a primary key in another table, and a secondary key is a non-unique field used to search or sort records efficiently.
• An entity–relationship model represents entities, their attributes and the one-to-one, one-to-many or many-to-many relationships between them; many-to-many relationships are implemented using a linking entity.
• Normalisation organises relational data to reduce redundancy and update anomalies: 1NF removes repeating groups and requires atomic values, 2NF removes partial dependency on a composite key, and 3NF removes transitive dependency between non-key attributes.
• An index is an additional data structure that speeds up searching and sorting on selected fields, but it requires extra storage and must be updated when records change.
• Data can be captured through methods such as forms, sensors, barcode readers and file imports; database queries select data, a database management system manages it, and standard formats or network protocols allow it to be exchanged.
• Referential integrity requires every foreign-key value to match an existing primary-key value in the referenced table, or to be null where null values are permitted.
• A transaction is a complete logical unit of database work, and ACID means Atomicity ensures all operations complete or none do, Consistency preserves database rules, Isolation prevents concurrent transactions interfering, and Durability preserves committed changes.
• Record locking restricts simultaneous access to records to prevent conflicting updates, while redundancy uses duplicate data, storage or systems to improve availability and recovery but can create inconsistency if poorly managed.
• A network connects devices so they can communicate and share resources, and agreed protocols and standards define rules such as data formats, addressing, transmission and error handling so different systems can interoperate.
• The TCP/IP stack uses the application, transport, internet and link layers; layering divides communication into manageable functions, and each layer provides services to the layer above it.
• DNS translates human-readable domain names into IP addresses; a LAN covers a limited geographical area, while a WAN connects devices or networks across a wider geographical area, often using third-party infrastructure.
• Packet switching divides data into addressed packets that may take different routes and be reassembled at the destination, whereas circuit switching reserves a dedicated end-to-end communication path for the duration of a connection.
• Network hardware includes network interface controllers that connect devices, switches that forward frames within a LAN, routers that forward packets between networks, wireless access points that provide wireless connectivity, and modems that convert signals for transmission media.
• In a client–server network, central servers provide services and control to clients, whereas in a peer-to-peer network each device can provide and consume resources; firewalls filter traffic, proxy servers act as intermediaries, and encryption protects intercepted data from unauthorised reading.
• HTML defines webpage structure and content, CSS controls presentation, and JavaScript adds behaviour; search engines discover pages with crawlers and build an index, PageRank estimates importance from incoming links and their importance, and processing may occur on the client or on a web server.

• Apply run-length encoding and dictionary coding to data, then calculate or compare the resulting file size and identify when each method is effective.
• Compare lossy and lossless compression for a given context, justifying the choice using reconstruction accuracy, file size and intended use.
• Explain and trace symmetric encryption, asymmetric encryption and hashing, identifying the keys used and selecting an appropriate technique for a security requirement.
• Construct an entity–relationship model that identifies entities, primary and foreign keys, attributes, cardinalities and any linking entities required to resolve many-to-many relationships.
• Normalise unstructured data to third normal form by creating atomic fields, removing partial dependencies and removing transitive dependencies while preserving valid relationships.
• Interpret and modify SQL statements that select, filter, sort, join, insert, update or delete relational data using the correct tables, fields and conditions.
• Apply referential-integrity and transaction-processing rules to database scenarios, explaining how ACID properties, record locking and redundancy protect data.
• Trace data through the TCP/IP stack, identifying the role of each layer, DNS resolution, relevant network hardware and the use of packet switching.
• Evaluate a network design or security scenario by selecting suitable hardware, architecture, protocols and controls such as firewalls, proxies and encryption, with reasons linked to the stated risks.
• Create and modify webpages using semantic HTML for structure, CSS for presentation and JavaScript for client-side behaviour, and distinguish these operations from server-side processing.