OLAP glossary
OLAP technology brings together a number of precise terms designating the elements of multidimensional structures. In addition, you will also come across several specific abbreviations in the OLAP world. We therefore need a glossary.
This glossary is only intended to illuminate, and is not a full and strict source of reference. Your (constructive) criticisms will help it to evolve.
Aggregate
The act of calculating values associated with parent positions in the hierarchical dimensions. This consolidation may be by addition, averaging or by other more complex processes like second strongest value.
Attribute
A fact describing each position of a dimension.
Axis
Synonym for dimension.
Cell
A piece of data defined by its position in each dimension. The cells of a hypercube can be empty or full. When a large number of cells are empty the data is said to be "sparse".
Cube
Most often a synonym for hypercube.
Data mart
The data relating to one of the jobs of the company. Several data marts form the data warehouse of the firm.
Data warehouse
A warehouse of data. Indicates all the data of the company, stored in a common data-processing form.
Dimension
A collection of data of the same type, allowing us to structure the multidimensional database. A dimension is sometimes referred to as an axis. In a measure, each cell of data is associated with one single position in each dimension. Time, Location and Product are the classic dimensions.
DOLAP
Desktop OLAP. Small OLAP products for local multidimensional analysis Desktop OLAP. There can be a mini multidimensional database (using Personal Express), or extraction of a datacube (using Business Objects).
Formula
A virtual hypercube. The values are often calculated on the fly, and not stored in the database.
Hierarchy
The positions of a dimension organised according to a series of cascading one to many relationships. This way of organizing data is comparable to a logical tree, where each member has only one parent but a variable number of children.
Hierarchy level
In a hierarchy, positions are classified into levels. All the positions for a level correspond to a unique classification. For example, in a "Time" dimension, level one stands for days, level two for months and level three for years.
HOLAP
Hybrid OLAP. Designates multidimensional analysis tools which store data in either relational or multidimensional databases, in a transparent way for the user.
Hypercube
A multidimensional construction formed by the conjunction of several dimensions. Each cell is defined by a single member of each dimension.
MDB
Multidimensional database. Allows storage, manipulation and reproduction of multidimensional data.
Measure
A hypercube, most often an integer or decimal type, structured by the dimensions. Salary, Value and Quantity are classic measures.
MOLAP
Multidimensional OLAP. This term designates a cartesian data structure more specifically. In effect, MOLAP contrasts with ROLAP. Inb the former, joins between tables are already suitable, which enhances performances. In the latter, joins are computed during the request.
Multicube
A multidimensional construction formed from several hypercubes sharing certain dimensions.
Multidimensional
Data structure having at least three independent dimensions.
OLAP
Literally, On-Line Analytical Processing. Designates a category of applications and technologies that allow the collection, storage, manipulation and reproduction of multidimensional data, with the goal of analysis. Another definition is contained in the acronym FASMI (Fast Analysis of Shared Multidimensional Information). OLAP tools have to follow 12 rules, described on this page.
Position
A value of a dimension. Also called a dimension member.
RDBMS
Relational database Management System. Allow storage, manipulation and reproduction of data stored in relational tables. The french equivalent is SGBDR.
Relation
A relation between the positions of two dimensions is a good way to make on-the-fly calculations, and thus easily create formulas.
ROLAP
Relational OLAP. Designates one or several star schemas stored in relational databases. This technology permits multidimensional analysis with data stored in relational databases.
Star schema
Arrangement of data in a relational database. In the middle is the fact table, whose columns constitute the multidimensional measures. The branches of the star, which radiate from the fact table, correspond to the dimensions. The conceptual data model represents this star schema.
Variable
Normally a synonym for measure.