HSC Enterprise Computing cheat sheet

Enterprise computing systems are large-scale, integrated IT environments that support core organisational processes across many departments and sites, distinguished from single-purpose systems by scale, integration and mission criticality.

System categories by role: transaction processing systems record high-volume day-to-day events; management information systems summarise transaction data into reports; decision support systems add modelling and what-if analysis; executive information systems present high-level indicators.

Data hierarchy: a field is one attribute, a record is a set of related fields, a file is a set of related records, and a database is an integrated collection of related files managed to reduce redundancy and inconsistency.

DBMS functions: data definition, data manipulation, concurrency control, integrity enforcement, security authorisation, backup and recovery, and transaction logging; a relational DBMS stores data in tables linked by keys.

Primary key uniquely identifies a record; foreign key is an attribute in one table matching the primary key of another and enforces referential integrity; normalisation organises attributes into tables to remove repeating groups and update anomalies.

ACID properties of a transaction: Atomicity (all or nothing), Consistency (valid state to valid state), Isolation (concurrent transactions do not interfere), Durability (committed changes survive failure).

Client-server places presentation logic on clients and data or business logic on servers; n-tier architecture separates presentation, application and data layers so each can scale or be replaced independently.

Virtualisation runs multiple logical servers on one physical host, improving hardware utilisation and enabling rapid provisioning; cloud service models are IaaS (infrastructure), PaaS (platform) and SaaS (application), with deployment models private, public, hybrid and community.

Network and security controls: firewalls filter traffic by rule, VPNs encrypt remote sessions, authentication verifies identity, authorisation grants access rights, and encryption protects data at rest and in transit.

Project phases follow a life cycle: initiation, planning, execution, monitoring and control, and closure; each phase produces deliverables and a decision point (gate) before the next begins.

Project triangle (triple constraint): scope, time and cost are interdependent; a change to one affects the others, and quality sits at the centre as the outcome of balancing them.

Scope statement defines deliverables, boundaries and acceptance criteria; a scope change must pass change control (request, impact assessment, approval, update to baseline) to prevent scope creep.

Work breakdown structure (WBS) decomposes deliverables into work packages; each package supports estimation of effort, duration, cost and assignment of responsibility.

Scheduling tools: a Gantt chart shows tasks against a calendar and displays duration and overlap; a network diagram (PERT/CPM) shows dependencies and identifies the critical path, the longest dependent sequence with zero float.

Float (slack) = late start minus early start (or late finish minus early finish); activities on the critical path have zero float, so any delay there delays the whole project.

Cost and effort estimation techniques include top-down (analogous), bottom-up (from WBS), parametric (rate per unit) and three-point (optimistic, most likely, pessimistic) estimates; each estimate should state its assumptions.

Risk management cycle: identify risks, assess likelihood and impact (risk exposure = probability x impact), plan responses (avoid, reduce, transfer, accept), then monitor and review throughout the project.

Quality and stakeholder control: a quality plan sets standards and review points; validation confirms the right product is built, verification confirms it is built correctly; sign-off by the client marks acceptance of deliverables.