Alia Flashcards
What does NoSQL stand for?
Not Only SQL
NoSQL Comprimises
Mostly not ACID
Some are BASE
Compared with SQL, sometimes limit capabilities for Queries and Updates
What does ACID stand for
Atomicity
Consistency
Isolation
Durability
Define: Atomicity
Requires that all transactions are “All or nothing” If one part fails, then the entire transaction fails
Define: Consistency
Ensures that any transaction will bring the database from one valid state to another
Define: Isolation
Ensures that concurrent execution of transactions happen one after the other
Define: Durability
Once a transaction has been committed, it will remain. Even in the event of a power loss or other critical failure
What does BASE stand for
Basically Available
Soft State
Eventual Consistency
Define: Basically Available
The database appears to work most of the time
Define: Soft state
Stores don’t have to be consistent over time
Define: Eventual Consistency
Will be consistent at some point in time
What is Linked Data
Linked Open Data denotes publicly available RDF data in the web, identified via URI
What is URI
Uniform Resource Identifier, it defines a simple and extensible schema for worldwide unique identification of abstract or physical resource
What does RDF stand for
Resource Description Framework
What is RDF
Resource
- Can be anything
- must be uniquely identified via URI
Description
- description of the resource
- via representing properties and relationships among
resources as graphs
Framework
- combination of web based protocols (URI, HTTP,
XML, etc)
- based on formal model
Properties of RDF Statements
They’re triples
Subject + Property + Object/Value
URI URI URI/Literal
What are URIs and Literals
URIs reference resources uniquely
Literals describe data values that don’t have a separate existence e.g. 1939
What are RDF Lists
General data structure used to enumerate any resource or literal. Can be a “Container” or a “Collection”
Define: Container
Open list, i.e. extension possible
Define: Collection
Closed list, i.e. no extension possible
Define: Reification
RDF allows the interleaving of statements, i.e. to make statements about statements
What is the use of reification
Used to model data provenance, formalise statements about reliability and trust, and define metadata about statements
What are the drawbacks of reification
Relations can be transformed into classes/instances (type conflicts), and infinite recursions can occur
Define: vocabulary
provide agreed, unambiguously-defined terms
Define: Taxonomies
add a hierarchical organisation
Define: Ontologies
Add richer knowledge
What are RDF Semantics
In contrast to other data definition languages, RDF(S) is based on a formal semantics. These enable RDF(S) to draw valid and sound logical inferences
What are vocabularies used for
classify the terms that can be used in a particular application
characterise possible relationships
define possible constraints on using those terms
How to represent Ontologies
Can be represented via classes, relations, and instances
What are classes
Classes are abstract groups, sets, or collections of objects and represent ontology concepts. They are characterised via attributes
What are attributes
Name-value pairs
What are relations
Relations are special attributes, whose values are objects of other classes
