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On Querying Versions of On Querying Versions of Multiversion Data Warehouse Multiversion Data Warehouse
Tadeusz MorzyTadeusz Morzy
Robert WrembelRobert Wrembel
Poznań University of TechnologyPoznań University of Technology
Institute of Computing ScienceInstitute of Computing Science
Poznań, PolandPoznań, Poland
[email protected]@cs.put.poznan.pl
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 2
Presentation OutlinePresentation Outline
Context and motivation of our work
Related work
Contribution The concept of a multiversion data warehouse
Querying a muliversion data warehouse
Ongoing and future work
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 3
Context and Motivation Context and Motivation (1)(1)
The research area encompases handling dynamics of EDSs in a DW (by means
of applying a MVDW) querying a MVDW
Dynamic nature of EDSs data dynamics
user data processing in EDSs DW refreshing
schema dynamics new user requirements dynamic nature of a real world tuning purposes require changes to EDSs schemas
changes to DW structure
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 4
European Union extension compare the sum of membership fees paid by the
countries in 2002, 2003, 2004 in 2004 – substantial increase did the countries pay
more in 2004? without the knowledge about EU extensions we could
end up with confusing conclusions
Context and Motivation Context and Motivation (2)(2)
EU
Belgium...
UK
T1 - 2002 T3 - 2004
Belgium...
UK
EU
PolandSlovenia
...
EU
T1 - 2003
Belgium...
UK
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 5
Sales analysis: reclassification of products to categories e.g., building elements changed tax from 7% to 22%
(Poland) compute and compare the sum of income from brick sales in
2003 and 2004 did sales of bricks increased 2004 by 15%? by simply updating brick’s vat from 7% to 22% we lose
information that in the past vat was 7%
Context and Motivation Context and Motivation (3)(3)
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 6
ChallengesChallenges
Dynamic nature of EDSs and real world should be reflected in a DW
New functionality of a data warehouse supporting changes of:
fact and level tables dimension instance structures
providing tools for appropriate analysis of data coming from different time periods
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 7
Related Approaches Related Approaches (1)(1)
Schema and data evolution [Blaschka et al., DaWaK99], [Hurtado et al.,
ICDE99, DOLAP99], [Koeller et al. DOLAP98]
Temporal extensions [Chamoni et al., DaWaK99], [Eder et al.,
DaWaK01, CAISE02], [Mendelzon et al., VLDB00]
Versioning implicit [Kang et al., VLDB02], [Quass et al.,
SIGMOD97], [Kulkarni et al, IDEAS99], [Teschke et al., DEXA98]
explicit [Bellahsene, DEXA98], [Body et al. DOLAP02]
virtual [Balmin et al., VLDB00]
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 8
The approaches assume that time is linear (DW states are ordered by time) true for past
Other LimitationsOther Limitations
not always true for future what-if analysis
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 9
Our ApproachOur Approach (1)(1)
Multiversion Data Warehouse MVDW is composed of a set of its versions changes in a DW structure and data reflected in a new
explicitly derived version of a DW DW Version
a schema version (facts, dimensions, levels, level instances)
an instance version (stores the set of data consistent with its schema version; measures/cell values)
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 10
Our ApproachOur Approach (2)(2)
Types of DW versions real
• reflects changes in real world• linearly ordered by time they are valid within• derived from another real version
alternative• created for simulation purposes (what-if analysis)• form DAG• derived from another real or alternative version
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 11
Data Model and ConceptsData Model and Concepts
Formal model of MVDW International Conference on Enterprise Information Systems
(ICEIS), France, 2003
Time integrity constraints for DW versions ACM Symposium on Applied Computing (SAC), Cyprus, 2004
Data sharing concept and evaluation 6th Baltic Conference on Databases & Information Systems,
Ryga, 2004 Conference on Current Trends in Theory and Practice of
Informatics (SOFSEM), Slovakia, 2005 (to appear)
Transaction concept International Conference on Enterprise Information Systems
(ICEIS), Portugal, 2004
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 12
Querying MVDWQuerying MVDW
Step 1 query decomposition PQ execution PR retrieval and
presentation Step 2
PR integration
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 13
MVQ User Interface MVQ User Interface (1)(1)
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 14
MVQ User Interface MVQ User Interface (2)(2)
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 15
Modes of Querying Modes of Querying (1)(1)
Querying the current DW version by default a user addresses the latest real DW version
Querying the set of real DW versions by specifying time period of interest, real versions are
valid within begin validity time - end validity time
select ...from ...where ...group by ...version from date 'begin date' to date 'end date'
select ...from ...where ...group by ...version from date 'begin date' to date 'end date'
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 16
Modes of Querying Modes of Querying (2)(2)
Querying the set of alternative DW versions a user has to explicitly provide a set of alternative
versions of interest
select ...from ...where ...group by ...alternative version in (ver_id | ver_name,..., )
select ...from ...where ...group by ...alternative version in (ver_id | ver_name,..., )
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 17
Modes of Querying Modes of Querying (3)(3)
Merging results of partial queries by default, every result set of a partial query is
presented to a user separately in some cases partial queries can be merged into one
result set merging the results obtained by partial queries is
defined by including the MERGE INTO clause
select ...from ...where ...group by ...version from date 'begin date' to date 'end date'merge into {ver_id | ver_name}
select ...from ...where ...group by ...version from date 'begin date' to date 'end date'merge into {ver_id | ver_name}
original partial results have to be transformed into a common schema transformation methods have to exist in the MVDW data dictionary
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 18
Modes of Querying Modes of Querying (4)(4)
Merging results of partial queries into a common DW version will be possible if a multiversion query addresses attributes that are
present in all versions of interest there exist transformation methods between adjacent
DW versions
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 19
Heterogeneous Schema Heterogeneous Schema VersionsVersions
Every version of a schema may have different structure problems in querying
Cases causing schemas heterogeneity handled by our prototype reclassification of level instances merging level instances splitting level instances level detachment level inclusion changing table name changing attribute name changing attribute domain dropping an attribute adding an attribute
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 20
Reclassification of level Reclassification of level instancesinstances
Result sets from RV2 and RV3 annotated with metadata information
Dimension PRODUCT: Level PRODUCT: change association: Ytong bricks (vat 7% vat 22%)Dimension PRODUCT: Level PRODUCT: change association: Ytong bricks (vat 7% vat 22%)
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 21
Merging level instancesMerging level instances
Result sets from RV3 and RV4 annotated with metadata information
Merge (Castorama, Marx Pipes) CastoramaMerge (Castorama, Marx Pipes) Castorama
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 22
Level DetachmentLevel Detachment
Result sets from RV4 and RV5 annotated with metadata information
Dimension Shop: level detachment CityDimension Shop: source attribute: Shop.city_name City.city_name
Dimension Shop: level detachment CityDimension Shop: source attribute: Shop.city_name City.city_name
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 23
Changing table/attribute nameChanging table/attribute name
Result sets from RV5 and RV6 annotated with metadata information
Table name changing: Sale Poland_SaleAttribute name changing: City.city_name City.cityTable name changing: Sale Poland_SaleAttribute name changing: City.city_name City.city
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 24
Changing attribute domainChanging attribute domain
Hangling changes of attribute domains between DW versions
A forward and a backward conversion method has to be provided and registered in data dictionary Attr_Mappings.am_forward_meth_name Attr_Mappings.am_backward_meth_name
Conversion methods are implemented by a DW admin
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 25
Prototype LimitationsPrototype Limitations
All predicates of the SELECT command apply to all DW versions pointed to in the VERSION FROM and VERSION IN clauses it is not possible to express a predicate on a single DW version
The query parser is unable to infer appropriate versions of interest from the WHERE clause
The query parser is able to compute an integrated result set of a multiversion query using basic aggregate functions: SUM, MIN, MAX, AVG
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 26
MVDW MetamodelMVDW Metamodel
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 27
Ongoing WorkOngoing Work
Building a Multiversion DWMS a project supported from the Polish State
Committee for Scientific Research
DS1 DS2 DS3
ODS data integration and buffering detection of schema and data changes propagation of schema and data changes
MVQIMVQI
MVDWMMVDWM
ODSMODSM
Morzy T., Wrembel R.: On Querying Versions of Multiversion Data WarehouseDOLAP 2004 28
Open issues indexing multiversion data handling quality of information in a
MVDW
Future WorkFuture Work