Tutorial olap4j

OLAP4J - Introduction
Wanna be better than your opponentes ?
**Competitive advantage**
by @borjaeg

KEY POINTS
● MY PROBLEM (IN DREAMS)
● BUSINESS INTELLIGENCE
● WHAT IS OLAP ?
● WHAT IS OLAP4J?
● MAIN CLASSES/INTERFACES
● MDX
● SNIPPETS

MY PROBLEM
● Yeah! I have a discography, with many artists
from Spain and England. I want to get a hit this
summer, but now … I haven't got enough
money to bet on two different artists. Only
one. I need information from data, i need to
take advantage from other discographies...

BUSINESS INTELLIGENCE
● Business Intelligence (BI) is the ability of an organization
to collect, mantain, and organize data.
● Large amounts of information can help develop new
opportunities.
● Identifying them, can provide a competitive market
advantage and long-term stability.
● Technology → OLAP, Data Mining, predective analytics...

WHAT IS OLAP ?
● In computing science (installing printers is not included),
online analytical processing, or OLAP, is an approach to
answering multi-dimensional analytical queries swiftly.
● OLAP is an important part of Business intelligence.
● Main concepts (for me ^^) → Hypercube, dimensions,
meassures...
– ROLAP
– MOLAP
– HOLAP
– SOLAP
– ...

WHAT IS OLAP4J?
● JAVA API
● PROVIDES OLAP ANALISYS
● QUERY LANGUAGE
– MDX STRING
– MDX PARSE TREE
– METADA IS AT THE HEART OF Olap4j
– DIFFERENT CUBE SERVERS ARE SUPPORTED
● MSAS via XML/A
● MONDRIAN

MAIN CLASSES/INTERFACES
● Interfaces ...you should know them as they were your
girlfriend/hand.
– OlapConnection
– OlapWrapper
– OlapStatement/ PreparedOlapStatement
– CellSet
– CellSetAxis
– Position
– Cell

MAIN CASSES / INTERFACES
● Cellset is the set which contains the cell returned by the
MDX query.
● Cellset is the set where results are founded.
● What's a cell? (Next slide)
– Important API methods: getCell, getFilterAxis,
getMetadata...

● Cell is the structure which contains a part of the cellset.
Every cell, contains a part of the result we are searching
with a MDX query.
● It could be said that cells are as rows in RDBs or
documents in a document-oriented DB. This is just a very
simple approach, a really simple analogy.
– Important API methods: drillThrough, getValue,
isEmpty, isNull,...

● CellSetAxis is the axis of a cellset (OK?!!)
● A cell set has the same number of axes as the MDX
statement which was executed to produce it.
● Each axis is an ordered collection of members or tuples.
● Each member or tuple on an axis is called Position.
– Important API methods: getPositions, getAxisMetada...

● Position is one of the CellSetAxis objects in a CellSet.
● An axis has a particular dimensionality, that is, a set of
one or more dimensions which will appear on than axis,
and every position on that axis will have a member of
each of those dimensions. (Extracted from official API)
● WTF¿! → As The Beatles said “All you need are
snippets” (more or less...)
– Important API methods: getMembers, getOrdinal...

MDX
● Multidimensional Expressions (MDX) is a query
language for OLAP databases. Similar to SQL in RDBs
world. It is also a calculation language, with syntax similar
to spreadsheet formulas.
● Example (Next slide explain this query)

MDX
● Time dimension ON columns
● Artists dimension ON rows
● Results are filtered by Total Sales.
To solve my problem, I'm gonna visualize artists, the last
three summers and total sales.

SNIPPETS
● Environment where I'm working...and living.
– Macbook Pro
● Core i5 (2.54 Ghz)
● 16 GB RAM
– PostgreSQL 9.2
– Eclipse Juno (code is copied from Sublime)
● Index
– Getting connection
– Validating MDX query
– Executing MDX query and print results
– Executing a MDX query and go through all results.

SNIPPET I
Getting and closing Connection. I'm using some junit
annotations (v.4.11) and mondrian driver.

SNIPPET II
● Validating a query. In this snippet, it's also possible to
see how to parse a query. When you parse a query, you
can obtain the query model (rows, columns, filters...)

SNIPPET III
● Executing MDX query.
– executeOlapQuery
● Printing results.
– printQueryResult

SNIPPET IV
● Executing MDX query and going through results
– It's important to test if cells are empty. Doing some
operations with empty cells could throw
exceptions.

Conclusion
● Business intelligence is a “huge world” full of different
possibilities to get better information quality. This can also
be a problem. Each solution has advantages and
disadvantages.
● BI concepts aren't new. But nowadays most documents
which talk about BI are quite hard to undertands.
● My experience with Olap4j has been really good.
● Documentation is quite good, but it needed to be
improved with more examples.

Links recommended
● http://en.wikipedia.org/wiki/Business_intelligence
● http://en.wikipedia.org/wiki/Competitive_advantage
● http://en.wikipedia.org/wiki/Online_analytical_processing
● http://en.wikipedia.org/wiki/MultiDimensional_eXpression
s
● http://mondrian.pentaho.com/
● http://www.olap4j.org/

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