1. 28th IEEE International Conference on Data Engineering (ICDE)
Washington, DC, USA, April 1-5, 2012
A meta-language for MDX
queries in eLog Business Solution
Sonia Bergamaschi*, Matteo Interlandi*, Mario Longo°,
Laura Po*, Maurizio Vincini*
*Department of Computer Engineering University of Modena & Reggio Emilia
°eBilling S.p.A.
2. eLog
• eLog, a business intelligence solution re-designed and
upgraded jointly with the database group of the University
of Modena and Reggio Emilia and eBilling
• eBilling - an Italian SME supplier of solutions for the
design, production and automation of documentary
processes for top Italian companies.
• Over 140 medium and large companies
• Sky, Mediaset, H3G, Tim Brazil
• In a period of 18 months 150 millions mail pieces = 1 TB of
data
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
3. BCPortal
• The BCPortal® framework core consists of several modules
for generating, delivering, managing company business
communications.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
5. Toward a multidimensional approach
transactional system
multidimensional system
• MDX is very powerful and effective but unfeasible for
unskilled users
semi-static reporting: an intermediate
approach between static reporting and OLAP
eLog - the new version
the decision maker
- is autonomous in the process of
creating, managing and sharing new analysis
- can intuitively define new indicators and
aggregate functions
Meta-language
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
6. Key features
• Simple GUI - all the complexities are masked by the underlying
system.
• Data conceptualization - a set of XSD schemas (for defining
mapping between cube attributes and visualized attributes)
decouple the GUI and the OLAP server
• Modular and reusable software – MDXGenerator is a stand-alone
java library, OLAP engine independent.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
7. GUI
Save and load functionalities
Predefined and custom attributes
Laura Po
4 quadrants the user fills with
attributes in order to create
the desired query
"A meta-language for MDX queries in eLog Business Solution"
8. Data Conceptualization
• Each pivot configuration is codified in a set of XML files
that will be the input of the MDXGenerator component.
• Each XML
configuration
conforms to an high
level
conceptualization
implemented in a
XML Schema (XSD)
• 9 XSD schemas, each
of which models a
particular part of the
pivot configuration.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
9. MDX Generator
• A standalone library that provides functionalities for
automatic multidimensional queries generation starting
from a XML pivot configuration.
• It is also responsible for
• the syntactic verification of the pivot configuration
• the semantic correctness of the MDX expression
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
10. Syntactic verification
• syntactic verification of the pivot
configuration
• the input is verified to be
syntactically well formed,
• it is divided in subsections of
interest and parsed,
• six different structures are filled
with the elements extracted from
the pivot configuration
• Data Cubes
• Data Attributes
• 4 structure, one for each quadrant.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
11. Semantic correctness
• semantic correctness of the MDX expression
• For every custom attribute, it performs on-the-fly
translation of the meta-language expression
into MDX.
• It verifies that the elements contained in the
configuration can be mapped into the data schema
on the OLAP server.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
12. MDX query
• MDXGenerator starts the composition of the final
query: a java object containing strings for each section
of the MDX query
SELECT
It is filled wrapping the information
from the 6 structures with MDX
language constructs
FROM
WHERE
It contains a list of cubes – then, the
Cube Selection algorithm choses the
best cube and consequently
reassembles the query
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
13. Meta-language &
custom attributes definition
• a simplified version of the MDX language both in semantics
and syntax
• the requirements were defined by eBilling after an analysis
conducted on the KPIs.
• multiple versions of the meta-language for the different
localizations
The main features are:
• a list of functions to combine and manage attributes
values;
• the hierarchy management, to create new members inside
a hierarchy or new hierarchies embracing a subset of
members in a hierarchy
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
14. Number, Constant, MDX Entity, Expression
• Number
• Constant - any sequence of characters and (potentially)
numbers
• MDX Entity - any member belonging to a dimension inside
a cube
• Expression can be of three types:
• Arithmetic Expression arithmetic operators (“+”, “-”, “*”, “/”)
• Comparison Expression relational operators (“ >”, “ <”, “ =”, “
>=”, “ <=” “ <>”)
• Logic Expression logic operands separated by “AND”, “OR”,
“XOR” and “NOT” operators.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
15. Functions
• The functions that have been implemented in order to
combine and manage values within the measures (and
dimensions) are the following:
• format, if, concat, contains, current, previous, following
• create hierarchy
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
16. Example
This Dimensional Fact
Model represents the
monitoring activity of the
SLA related to some mail
pieces, called missives.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
17. Example – new member inside a hierarchy
• Query : for the first and
the second quarter of each
year, compute for every
client and for the cities of
Naples and Rome, the
number of missives in SLA
and the total number of
missives that are both in
SLA and out SLA.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
18. Define a new custom attribute
XML file
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
19. Define the pivot configuration
• Query : for the first
and the second
quarter of each
year, compute for
every client and for
the cities of Naples
and Rome, the
number of missives
in SLA and the total
number of missives
that are both in SLA
and out SLA.
MDXquery
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
20. Moreover…
To improve time-performance:
• Cache – MDXGenerator
• Already parsed configurations are stored in a cache
• If a pivot configuration is stored in memory, the data can be
retrieved directly from the cache, thus decreasing the query
generation time
• Cube Selection
• The Cube selection is an algorithm that chooses among all the
cubes contained in the pivot configuration the optimal one for
the execution of the query
• The algorithm has been designed to be as general as possible
and completely independent on the input cubes.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
21. Test
• 15 typical queries from a minimum of 3 dimensions to a
maximum of 8 different dimensions (a typical pivot analysis)
• 8.974.662 facts (related to 8 months of eLog’s data production) Btree index for the foreign keys on the fact table
• concurrent access for up to 25 users
Exploiting the cache outperforms by 7 times the
performance of the MDXGenerator
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
22. Conclusion
• New version of eLog: the business intelligence solution of
eBilling for document management
traceability, optimization and analysis.
transactional system
multidimensional system
Data model conceptualization: XSD schemas
MDX Generator – a stand alone library
Customized attributes – Meta-language
Cache (pivot configurations)
Cube Selection algorithm
Laura Po
}
}
middle layer
between the
framework and
the OLAP
engine
optimization of
the query
"A meta-language for MDX queries in eLog Business Solution"
23. Future Work
• To extend the compliance of MDX language also for
Microsoft SQL Server (so far, it is compliant with Mondrian
system).
• More experiments on the use of the eLog system on
customer data.
• To investigate how MDXGenerator can be enhanced to
improve the query rewriting for optimizing the query
processing
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
24. Thanks for your attention
• Contacts:
• just type «Laura Po» at Google.com
• laura.po@unimore.it
• DBGROUP
• www.dbgroup.unimo.it
• Ebilling
• www.ebilling.it
• Download this presentation:
• http://www.dbgroup.unimo.it/~po/pubs.html
• or http://db.tt/1aJsuTJo
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
25. Cube Selection
• The query object created by the MDXGenerator contains in
the FROM field all the cubes that might be used.
• The Cube selection is an algorithm that chooses among all
the cubes contained in the pivot configuration the optimal
one for the execution of the query
• The algorithm has been designed to be as general as
possible and completely independent on the input cubes.
• it is not mandatory that the input cubes share the same
semantic structure
• in eLog each of the input cubes takes into consideration
different portion of the schema containing data at different
granularity
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
26. Cube Selection
Given
• S(C,D) schema
• C the set containing all the cubes
• D the set of all dimensions
• Q the query derived from the pivot table configuration,
• L the set of all the distinct levels belonging to at least one
dimension contained in the set D
we define
• QL’ the query that involves the non empty set L’ of hierarchical
levels of dimensions, where L’ L and CL[l] the not empty subset
of C containing the cubes where the dimension of the level l L is
used.
• |c| the number of dimensions in the cube c
• co the cube containing all the levels with lowest granularity.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
27. Semantic correctness
• semantic correctness of the MDX expression
• For every custom attribute, it performs on-the-fly
translation of the meta-language expression into
MDX.
• During the meta-language translation, the solve order
sequence is automatically defined following the position in
the quadrant, chosen by the user
• It verifies that the elements contained in the
configuration can be mapped into the data schema on
the OLAP server.
Laura Po
"A meta-language for MDX queries in eLog Business Solution"
