The standard column family is a

NoSQL NoSQL (originally meaning "Not only SQL" or "non-relational") refers to a type of database design that stores and retrieves data differently from the traditional table-based structure of relational databases. Unlike relational databases, which ...

object that contains

column A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member ...

s of related data. It is a

tuple In mathematics, a tuple is a finite sequence or ''ordered list'' of numbers or, more generally, mathematical objects, which are called the ''elements'' of the tuple. An -tuple is a tuple of elements, where is a non-negative integer. There is o ...

(pair) that consists of a key–value pair, where the key is mapped to a value that is a set of columns. In analogy with relational databases, a standard column family is as a "table", each key–value pair being a "row". Each column is a

( triplet) consisting of a column name, a value, and a

timestamp A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving date and time of day, sometimes accurate to a small fraction of a second. Timestamps do not have to be based on some absolu ...

. In a relational

database table In a database, a table is a collection of related data organized in table format; consisting of columns and rows. In relational databases, and flat file databases, a ''table'' is a set of data elements (values) using a model of vertical colum ...

, this data would be grouped together within a table with other non-related data. Standard column families are column containers sorted by their names can be referenced and sorted by their row key.

Benefits

Accessing the data in a

distributed Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...

data store A data store is a repository for persistently storing and managing collections of data which include not just repositories like databases, but also simpler store types such as simple files, emails, etc. A ''database'' is a collection of data that ...

would be expensive (time-consuming), if it would be saved in form of a table. It would also be inefficient to read all column families that would make up a row in a relational table and put it together to form a row, as the data for it is distributed on a large number of nodes. Therefore, the user accesses only the related information required. As an example, a relational table could consist of the columns UID, first name, surname, birthdate, gender, etc. In a distributed data store, the same table would be implemented by creating columns families for "UID, first name, surname", "birthdate, gender", etc. If one needs only the males that were born between 1950 and 1960, for a query in the relational database, all the table has to be read. In a distributed data store, it suffices to access only the second standard column family, as the rest of information is irrelevant.

Sorting and querying

There is no way to sort columns, nor to query an arbitrary query in

distributed data store A distributed data store is a computer network where information is stored on more than one node, often in a replicated fashion. It is usually specifically used to refer to either a distributed database where users store information on a ''numb ...

s. Columns are sorted when they are added to the column family. The way of sorting is defined by an attribute. For instance, this is done by the CompareWith attribute in

Apache Cassandra Apache Cassandra is a free and open-source software, free and open-source database management system designed to handle large volumes of data across multiple Commodity computing, commodity servers. The system prioritizes availability and scalab ...

that can have the following values: * AsciiType * BytesType * LexicalUUIDType * LongType * TimeUUIDType * UTF8Type It is also possible to add some user-defined sorting attributes. Using this way of sorting makes the process extremely quick.

Standard column families vs. rows

Standard column families have a schema-less nature so that each of their "row"s can contain a different number of columns, and even different column names could be in each row. So, they are a very different concept than the rows in relational database management system (RDBMS)s. This is one of the reasons why the concept is not trivial for an experienced RDBMS expert.

Examples

In JSON-like notation, a column family definition would look as follows: UserProfile = where "Cassandra", "TerryCho", "Cath" correspond to row keys; and "emailAddress", "age", "gender", "address" correspond to the column names.

References

{{reflist

External links