Karteikarten
Week 2 - Conceptual Modelling
Karten in diesem Stapel (11)
- 1ANSI/SPARC architecture: levels of data abstraction1. External => end-user view, hardware and software independent
2. Conceptual => global view of data and relationships, hardware and software independent
3. Internal => specific database model, hardware independent
4. Physical => storage and access methods, neither software nor hardware independent - 2Database life cycle 1: requirements definition- External level of ANSI/SPARC
- Identify and analyse user views e.g. report to be produced, transaction to be supported
- Output is a statement of specifications which describes the user views' requirements and constraints - 3Database life cycle 2: conceptual design- Conceptual level of ANSI/SPARC
- Independent of all physical implementation considerations
- Different design methodologies e.g. UML, ER (entity-relationship) model - 4Database life cycle 3: logical design- Internal level of ANSI/SPARC
- Select a specific model (e.g. relational, network, XML, NoSQL)
- Independent of implementation details specific to any particular DBMS package
- Normalisation is used to test correctness of a relational logical model - 5Database life cycle 4: physical design- Physical level of ANSI/SPARC
- Physical implementation of logical model
- Select specific vendor (e.g. Oracle, MySQL)
- Choose storage structures, indexes, file organisations and access methods to support user requirements - 6Components of ER diagram- Entities - objects of interest to end user
- Attributes - characteristics of entities - 7Types of attributes- Simple (atomic) vs composite
- Single-valued vs multi-valued => if multi-valued, can either split into new attributes (provided every instance has same number of values), or create new entity containing the multi-valued attribute's components
- Derived => calculated from other attributes - 8Connectivity, cardinality, degree- Connectivity - classification of relationship between entities e.g. 1:1, 1:M, M:N
- Cardinality - min and max number of allowed entity occurrences associated with one occurrence of the related entity
- Degree - number of entities associated with a relationship (unary, binary, ternary) - 9Strong vs weak entities- Strong entity - existence-independent (has a key which can be defined without reference to other entities)
- Weak entity - existence-dependent
and inherits the PK of its parent entity - 10Relationship strength: identifying vs non-identifying- Identifying relationship - identifier of related entity is part of the identifier of parent entity; shown with a solid line
- Non-identifying relationship - identifier of related entity is not part of the identifier of parent entity; shown with a broken line - 11Associative (composite) entity- Used to resolve an M:N relationship between two or more entities
- Associate entity is in a 1:M relationship with the parent entities and contains the PK attributes of each parent entity
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- Computer Science (FIT2094: Databases) Karteikarten am Week 2 - Conceptual Modelling, erstellt von Melina Mackey am 25/10/2020.
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- Melina Mackey
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- Erstellt von Melina Mackey · 19 Okt 2020
- Kopiert von Melina Mackey · 25 Okt 2020
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