A keyspace (or key space) in a
NoSQL
A NoSQL (originally referring to "non- SQL" or "non-relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed ...
data store is an object that holds together all
column families of a design. It is the outermost grouping of the data in the data store. It resembles the
schema concept in
Relational database management system
A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...
s.
Generally, there is one keyspace per application.
Structure
A keyspace may contain
column families or
super columns. Each super column contains one or more column families, and each column family contains at least one column. The keyspace is the highest abstraction in a
distributed data store. This is fundamental in preserving the structural heuristics in dynamic data retrieval.
Multiple relay protocol algorithms are integrated within the simple framework.
Comparison with relational database systems
The keyspace has similar importance like a
schema has in a database. In contrast to the schema, however, it does not stipulate any concrete structure, like it is known in the
entity-relationship model used widely in the
relational data models. For instance, the contents of the keyspace can be column families, each having different number of columns, or even different columns. So, the column families that somehow relate to the
row
Row or ROW may refer to:
Exercise
*Rowing, or a form of aquatic movement using oars
*Row (weight-lifting), a form of weight-lifting exercise
Math
*Row vector, a 1 × ''n'' matrix in linear algebra.
*Row (database), a single, implicitly structured ...
concept in relational databases do not stipulate any fixed structure. The only point that is the same with a schema is that it also contains a number of "objects", which are tables in RDBMS systems and here column families or super columns.
So, in distributed data stores, the whole burden to handle rows that may even change from data-store update to update lies on the shoulders of the programmers.
Examples
As an example, we show a number of column families in a keyspace. The
CompareWith keyword defines how the column comparison is made. In the example, the
UTF-8 standard has been selected. Other ways of comparison exist, such as
AsciiType,
BytesType,
LongType,
TimeUUIDType.
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Another example shows a simplified
Twitter clone data model:
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References
{{reflist
External links
Cassandra – Getting Started (Java)
Distributed data stores
NoSQL