IS5413 Chap.2 The Database Development Process and Schema Levels
The Database Development Process and Schema Levels
Database work is a strand, not a stage
The life cycle taught here attaches to every phase a purpose, an output, and a matching piece of database work, and the examinable point is the pairing rather than the list of phase names. Planning produces a request for study and begins enterprise modelling. Analysis produces the functional specification and is where conceptual modelling becomes thorough.
Logical design produces detailed design specifications and yields the logical database design, including views, integrity rules and security constraints. Physical design produces program and data structures and completes the physical database design, defining the database to the management system. Implementation produces operational programs and covers coding, installation and data conversion.
Maintenance produces periodic audits and covers performance analysis and tuning.
Read the deliverable to know what the activity can use
The deliverable column is not decoration. A request for study justifies a project and contains no entity types, which is why only enterprise level modelling can start there.
Functional specifications record the behaviour required of the system and the people it is required for, and that is the input a complete conceptual model depends on. Detailed design specifications cover transactions, forms and reports, and those are what external user views are cut from.
Reading across the row tells you what the database activity beside it can possibly be working with, and that is usually enough to place any activity a question offers you.
When the requirements will not hold still
The life cycle assumes requirements can be understood before anything is built.
Where they cannot, prototyping is offered as the classical rapid application development approach: conceptual modelling is deliberately cursory, a working version is built quickly, users evaluate it in operation, and the design is revised across successive versions. If a prototype proves inefficient the loop returns to physical design rather than to requirements.
Agile methods are named separately, with its stated preferences for people and conversation ahead of process and tooling, for working with the client ahead of negotiating the contract, and for adapting ahead of following a fixed plan, with extreme programming, Scrum and feature driven development listed as members of the family.
Three schemas, and why the middle one is single
External schemas are individual user views, each a subset shaped for one role.
The conceptual schema sets out the whole logical structure of the organisation's data as an entity relationship model, and there is exactly one of it. The internal schema is the physical storage and implementation detail.
Because every view is defined against the conceptual schema rather than against storage, storage can be reorganised without rewriting a single view, and a new view is cut from something that already exists rather than invented privately. That single middle layer is the mechanism behind the program data independence the previous chapter claimed as an advantage.
Note that the revision material sometimes calls the internal level the physical schema; both words name the same layer.
What this chapter covers
- 01
Six life cycle phases with their deliverables
- 02
The database activity that rides inside each phase
- 03
Prototyping as rapid application development
- 04
Agile as a family rather than a synonym
- 05
External, conceptual and internal schemas
- 06
Why one conceptual schema buys independence at both ends
Worked example · free
Place four activities in the right phase
- 2Place the security constraints and name the deliverable.
- 2Place the entity type list and name the deliverable.
- 2Place the table definitions and name the deliverable.
- 2Place the response time work and name the deliverable.
Key terms
- Systems Development Life Cycle
- A phased approach to building an information system in which every phase has a stated purpose, an output, and its own piece of database work.
- Prototyping
- A rapid development approach in which a working version is built quickly and refined through user evaluation, with the database defined and re evolved across successive versions.
- External Schema
- One user view of the data, tailored to a role and defined as a subset of the conceptual schema rather than against physical storage.
- Conceptual Schema
- The whole logical structure of the organisation's data, set out as an entity relationship model. Exactly one exists, which is what makes the outer layers independent.
- Internal Schema
- The physical storage and implementation detail of the database. The revision material also calls this the physical schema; both names refer to the same layer.
The Database Development Process and Schema Levels FAQ
When does conceptual data modelling actually start?
It starts in the planning phase as enterprise modelling, at a high level and without attribute detail, and becomes thorough in the analysis phase once functional specifications exist. Saying that it starts in analysis is the common half answer; saying it starts in design is wrong, because by design the model is already being converted.
The distinction matters because it tells you what input each version of the model had available.
Is prototyping the same thing as agile development?
No. The course presents prototyping as the classical rapid application development approach, a specific loop of build, evaluate and revise in which the database is defined across successive versions. Agile is introduced separately as a family of methods with its own statement of values, including extreme programming, Scrum and feature driven development.
Treating the two as interchangeable loses the distinction a question is likely to be testing.
What problem does the three schema architecture solve?
It makes the storage layer and the user view layer independent of each other. Every external view is defined against a single conceptual schema rather than against storage, so files can be reorganised, indexed or moved without any view being rewritten, and a new view can be cut from a structure that already exists. Remove the single middle layer and both guarantees disappear at the same time.
Exam move
Draw the six phase table from memory with three columns, phase, deliverable and database activity, and check it against the chapter. Then practise the reverse direction, which is how questions are usually set: given an activity, name its phase and its deliverable.
Finish by writing one sentence explaining how the three schema architecture delivers program data independence, since that link is the most common essay style question in this material.
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