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Database Architectures

The Theoretical Fifth Generation

The Three Schema Architecture of a Theoretical Fifth Generation Information System

The basis for the theoretical fifth generation database system is the conceptual layer. At the heart of this system is the conceptual information processor (CIP). The user transacts with the external layer, transactions are passed to the conceptual layer and the conceptual layer hands the actual storage to the internal layer.

3 schema architecture

i = internal structures (integers, records, trees etc)
s = elementary sentences (facts)
e = external structures (menus, tables, graphs, 'natural' language queries)

  1. INTERNAL = the data stored in binary on disk (IB); DOS, say (IP); DOS file format conventions (CS)
  2. CONCEPTUAL = Facts stored somehow (IB); CIP; Conceptual Schema
  3. EXTERNAL = users 'view' of DB (tables or reports); IB = 'Friendly front-end'(application software); IP = Menu structure? program organisation

The true power of this model lies in the relative independence of the system - when such a system is implemented on different hardware to that it was originally designed for, ONLY INTERNAL structures need re-writing, the rest stays as is.

IS Interactions

  1. Queries - answers from constraints - answers from IB (fact retrieval) - derived facts (combining facts to form new facts) --> all answers subject to CIP approval
  2. Updates - either ADD a sentence (instance of a fact type) or DELETE a sentence (to modify, we delete and replace a sentence), also add and remove fact types and constaints.

Updates can be SINGLE transactions, or may involve PARCELS of requests (so long as at the end of the 'parcel', IB is in a valid state, then Parcel transaction is accepted)


Software Development Cycle

  1. Specification - what the software is supposed to do.
  2. Design - plan to meet specification, algorithms and conceptual ideas
  3. Implementation- using developmental tools (eg. languages)
  4. Testing - every facet trialled, once 'bug free' then beta testing, then release
  5. Maintenance -corrective (fixing bugs); adaptive (alterations to suit users); perfective (improvements)

3GLs- most time taken up with implementation/testing

4-5GLs -most time needed in specification and design

We will learn ORM (Object Role Modelling) (invented by Nijssen, Falkenberg & Halpin - also called NIAM), also known more recently FORML

  • Fact based analysis which attempts to describe UoD starting with specific examples.
  • procedure well defined, and uses a standardised diagramming method.
  • once the Conceptual Schema diagram is complete, it is translated into a relational schema (table design) that is correct and redundancy free (and in OPTIMAL NORMAL FORM)
 

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