from uml to rolap multidimensional databases using a pivot model

N.PRAT, J.AKOKA – BDA 2002

From UML to ROLAP From UML to ROLAP multidimensional databases multidimensional databases

using a pivot modelusing a pivot model

Nicolas PRAT, ESSEC Business SchoolNicolas PRAT, ESSEC Business SchoolJacky AKOKA, CNAM ParisJacky AKOKA, CNAM Paris

BDA 2002, INT, Evry, October 2002 BDA 2002, INT, Evry, October 2002

N.PRAT, J.AKOKA – BDA 2002 2

OverviewOverview

1. Introduction1. Introduction 2. Unified multidimensional metamodel2. Unified multidimensional metamodel 3. Design method3. Design method 4. Conclusion4. Conclusion


IntroductionIntroduction Data warehousing and OLAP market growing rapidlyData warehousing and OLAP market growing rapidly

=> need for systematic, tool-supported method for data => need for systematic, tool-supported method for data warehouse/multidimensional database design.warehouse/multidimensional database design.

Difficulty of data warehouse design often Difficulty of data warehouse design often underestimated by OLAP tool vendors. However, underestimated by OLAP tool vendors. However, crucial phase.crucial phase. =>=>

Data warehouse design should follow the Data warehouse design should follow the conceptual/logical/physical design phases (as in conceptual/logical/physical design phases (as in transactional database design).transactional database design).

1. Introduction


State of the artState of the art Many papers proposing multidimensional data models (sometimes Many papers proposing multidimensional data models (sometimes

with associated algebra/query language).with associated algebra/query language).

Only a few data warehouse design methods (Akoka 97, Akoka 01, Only a few data warehouse design methods (Akoka 97, Akoka 01, Golfarelli 98, Cabibbo 98, Moody 00).Golfarelli 98, Cabibbo 98, Moody 00).

Distinction between conceptual/logical/physical:Distinction between conceptual/logical/physical: Often unclear and/or missing phases.Often unclear and/or missing phases.

Our contribution:Our contribution: Data Data warehousewarehouse designdesign method based on UML, spanning the three design method based on UML, spanning the three design

phases.phases. Metamodels for each Metamodels for each designdesign step step ((including unified multidimensional including unified multidimensional

metamodelmetamodel=>pivot model=>pivot model).). Transformations operating on the concepts of the metamodelTransformations operating on the concepts of the metamodelss.. Specification of the transformations in OCL (Object Constraint Language).Specification of the transformations in OCL (Object Constraint Language).

1. Introduction


Multidimensional metamodelMultidimensional metamodel Problem with the multidimensional Problem with the multidimensional metametamodel:model:

No agreement on the concepts of this model (e.g. facts).No agreement on the concepts of this model (e.g. facts). No agreement on the level of this model: physical, logical, or No agreement on the level of this model: physical, logical, or

conceptual.conceptual.

We consider the multidimensional We consider the multidimensional metametamodel to be at model to be at the logical level:the logical level: It exists independently of implementationIt exists independently of implementation.. Its concepts (e.g. dimension) are not as close to reality as Its concepts (e.g. dimension) are not as close to reality as

concepts like the object or the entity.concepts like the object or the entity. Strong parallel with the relational model.Strong parallel with the relational model.

We have defined a unified multidimensional model.We have defined a unified multidimensional model.

2. Unified multidimensional metamodel


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6 8 11 5 9 9

P1 P2 P3 P4 P5 P6 P7

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9 March 99

BordeauxBrest

LyonNantes

Paris

LEGEND

Multidimensional modelingMultidimensional modeling

CATEGORY

:

product nameunit price

Attribute

PRODUCT

DA

Y

DIMENSION

CITY

REGION

Measure

Quantity sold

MO

NT

H

QU

AR

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R

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Hierarchy

2. Unified multidimensional metamodel


Unified multidimensional metamodelUnified multidimensional metamodel2. Unified multidimensional metamodel

AggregateFunction

name : FunctionNamerestrictionLevel : Integer

AggregateFunction

name : FunctionNamerestrictionLevel : Integer

1..*

0..*

1..*

0..*

1..*

0..*

1..*

0..*

Measure

dummyMeasure : Boolean

Measure

dummyMeasure : Boolean

DimensionAttributeDimensionAttribute

1..*

0..*

+dimension

1..*

+measure0..* Dimensioning

strong : Boolean

Dimensioning

strong : Boolean

1..*

0..*

+dimension

1..*

+measure0..*

DimensionDimension

+ +owner

1attribute

0..*DimensionHierarchyDimensionHierarchy

++source1dimensionLink 0..*

DimensionLinkDimensionLink

+target dimensionLink 0..*1

1..*2..*

+dimensionHierarchy1..*

+dimensionLink

2..*

{ordered}

1..*2..*

++

{ }dimensionHierarchy

1..*dimensionLink

2..*

ordered

level : Integerlevel : Integer

ModelElement

name : Name

ModelElement

name : NameMultidimensionalModelMultidimensionalModel

MultidimensionalModelElementMultidimensionalModelElement

11..*

1+ownedElement1..*

11..* +


OverviewOverview3. Design method

Universe of discourseUniverse of discourse

CONCEPTUALDESIGN

CONCEPTUALDESIGN

LOGICALDESIGN

LOGICALDESIGN

PHYSICALDESIGN

PHYSICALDESIGN

DATACONFRON -

TATION

DATACONFRON -

TATION

UML schema

conceptual modeling

UML model

conceptual modeling

enrichment /transformation

Enriched /transformed UML schema

enrichment /transformation

Enriched /transformed UML model

Logical mapping

Unified multidimensional schema

Logical mapping

Unified multidimensional model

Physical mapping

ROLAP snowflakeschema

ROLAP star

schema

MOLAPschema

Physical mapping

Source confrontation

Data Warehouse Metadata

Source confrontation

Data Warehouse Metadata


Conceptual designConceptual design Multidimensional representation of data (OLAP).Multidimensional representation of data (OLAP).

Conceptual phase necessary (vs. direct representation of data in Conceptual phase necessary (vs. direct representation of data in ROLAP stars/snowflakes or MOLAP cubes).ROLAP stars/snowflakes or MOLAP cubes).

Choice of UML for the conceptual phase:Choice of UML for the conceptual phase: Standard and well-known formalismStandard and well-known formalism Simple and powerful constructs to represent data at a high level of Simple and powerful constructs to represent data at a high level of

abstractionabstraction ““Easy” mapping to relational and multidimensional systems.Easy” mapping to relational and multidimensional systems.

2-step conceptual design:2-step conceptual design: Definition of a UML model (class diagram without operations)Definition of a UML model (class diagram without operations) Enrichment/transformation of this model to facilitate further automatic Enrichment/transformation of this model to facilitate further automatic

mapping to a unified multidimensional model.mapping to a unified multidimensional model. =>need to enrich UML metamodel.=>need to enrich UML metamodel.

3. Design method


Enriched UML metamodelEnriched UML metamodel3. Design method

ModelElementname : Name

Relationship

AttributeOfOrdinaryClass

identifyingAttribute : Boolean

AttributeOfAssociationClass

OrdinaryClass AssociationClass OrdinaryAssociation

GeneralizationConstraint

UMLModel

Constraint

UMLModelElement

1

1..*

1

+ownedElement1..*

0..*0..*

+constraint

0..*+constrainedElement

0..*{ordered}

Association

Attributemeasure : Boolean

AssociationEnd

aggregation:AggregationKindmultiplicity : Multiplicity

11

2..* {ordered}

Generalization

Class1 0..*

+owner

1

+attribute

0..*{ordered}

0..*1

+association

0..*+participant

1

0..*

1

+specialization

0..*

+parent1

0..*

1+generalization

0..*

+child1

{disjoint,complete}

{disjoint,complete}

{disjoint,complete}

+connection

+association

ModelElementname : Name

Relationship

AttributeOfOrdinaryClass

identifyingAttribute :Boolean

AttributeOfAssociationClass

OrdinaryClass AssociationClass OrdinaryAssociation

GeneralizationConstraint

UMLModel

Constraint

UMLModelElement

1

1..*

1

+ownedElement1..*

0..*0..*

+constraint

0..*+constrainedElement

0..*{ordered}

Association

Attributemeasure :Boolean

AssociationEnd

aggregation:AggregationKindmultiplicity : Multiplicity

11

2..* {ordered}

Generalization

Class1 0..*

+owner

1

+attribute

0..*{ordered}

0..*1

+association

0..*+participant

1

0..*

1

+specialization

0..*

+parent1

0..*

1+generalization

0..*

+child1

{disjoint,complete}

{disjoint,complete}

{disjoint,complete}

+connection

+association


Conceptual Conceptual design design ((stepstep 11))

3. Design method

percentage_of_region

Private_ shareholder Public_ shareholderpublic_ shareholder_level

Person Company

manager_name

exposure

media_exposure

Year

year

Datedd_mm_yy

Media_type

media_typeinsertion

Shareholdershareholder_name

Region

regionnumber_of_ inhabitants

Quarter

quarter

11..*11..*

11..*

11..*

consumptionproduct_ consumption

Mediamedia_nameadvertising_price

1

*

1

*

1

*

1

*main_

shareholder

*

1..*

*

1..*gets

Product_type

product_typeproduct_unit *1..* *1..*

may_be_ advertised_in

Targettarget_codestatusminimum_agemaximum_age

sex

1..*

1

1..*

1

*

*

*

*

Advertising_ campaign

campaign_code

1

*

1

*

during

*

*

*

*

is_ strongly_ influenced_by

1..*

*

1..*

*

in

Product

product_codeproduct_name

1

*

1

*

*

*

*

*

*

1

*

1

for

**

*

percentage_of_region

Private_ shareholder Public_ shareholderpublic_ shareholder_level

Person Company

manager_name

exposure

media_exposure

Year

year

Datedd_mm_yy

Media_type

media_typeinsertion

Shareholdershareholder_name

Region

regionnumber_of_ inhabitants

Quarter

quarter

11..*11..*

11..*

11..*

consumptionproduct_ consumption

Mediamedia_nameadvertising_price

1

*

1

*

1

*

1

*main_

shareholder

*

1..*

*

1..*gets

Product_type

product_typeproduct_unit *1..* *1..*

may_be_ advertised_in

Targettarget_codestatusminimum_agemaximum_age

sex

1..*

1

1..*

1

*

*

*

*

Advertising_ campaign

campaign_code

1

*

1

*

during

*

*

*

*

is_ strongly_ influenced_by

1..*

*

1..*

*

in

Product

product_codeproduct_name

1

*

1

*

*

*

*

*

*

1

*

1

for

**

*

{overlapping,complete}

{disjoint,complete}


Conceptual design (Conceptual design (stepstep 2) 2) Enrichment/transformation of the UML Enrichment/transformation of the UML modelmodel with 4 with 4

types of successive types of successive transformationstransformations:: Determination of identifying attributesDetermination of identifying attributes Determination of attributes representing measuresDetermination of attributes representing measures Migration of association attributesMigration of association attributes TransformationTransformation of generalizations. of generalizations.

Determination of identifying attributes:Determination of identifying attributes: Identifier=not a standard concept in UMLIdentifier=not a standard concept in UML Necessary in order to define dimensions in the logical phaseNecessary in order to define dimensions in the logical phase Necessary for ordinary classes onlyNecessary for ordinary classes only Use of the tagged value {id}.Use of the tagged value {id}.

3. Design method


Conceptual design (Conceptual design (stepstep 2) 2) Determination of attributes representing measures:Determination of attributes representing measures:

Measures vs. qualitative valuesMeasures vs. qualitative values Distinction cannot based performed automatically based on typesDistinction cannot based performed automatically based on types Not necessary for identifiers (defined previously)Not necessary for identifiers (defined previously) Use of the tagged value {meas}.Use of the tagged value {meas}.

Migration of 1-1 and 1-N association attributes:Migration of 1-1 and 1-N association attributes: Check validity of representation first. Check validity of representation first. Transformation Tcc3 : Each attribute belonging to a 1-1 association is Transformation Tcc3 : Each attribute belonging to a 1-1 association is

transferred to one of the classes involved in the association.transferred to one of the classes involved in the association. Transformation Tcc4 : Each attribute belonging to a 1-N association is Transformation Tcc4 : Each attribute belonging to a 1-N association is

transferred to the N-class, i.e. the class involved several times in the transferred to the N-class, i.e. the class involved several times in the association.association.

TransformationTransformation of generalizations: of generalizations: No direct mapping of UML generalizations to multidimensional hierarchies. No direct mapping of UML generalizations to multidimensional hierarchies. UML generalizations transformed into aggregations and classesUML generalizations transformed into aggregations and classes..

3. Design method


Conceptual design (Conceptual design (stepstep 2) 2) Transformation of generalizations (cont’d):Transformation of generalizations (cont’d):

Transformation Tcc5 : For each level i of specialization of a class C, a class named Transformation Tcc5 : For each level i of specialization of a class C, a class named Type-C-i is created. The occurrences of these classes define all the specializations of C. Type-C-i is created. The occurrences of these classes define all the specializations of C. In case of overlapping between specializations, a special value is created for each In case of overlapping between specializations, a special value is created for each overlapping between two or more sub-classes of C. In case of incomplete overlapping between two or more sub-classes of C. In case of incomplete specialization, the special value “others” is created. A N-1 aggregation is created specialization, the special value “others” is created. A N-1 aggregation is created between the classes C and Type-C-i. between the classes C and Type-C-i.

3. Design method

Private_shareholder Public_ shareholder

public_shareholder_level

Person Company

manager_name

Private_shareholder Public_ shareholder

public_shareholder_level

Person Company

manager_name

{overlapping,complete}

{disjoint,complete}

Shareholder _type

shareholder_type {id}

Shareholder

shareholder_name {id}Transformation Tcc5

Shareholder_type


Shareholder

shareholder_name{id}public_shareholder_levelmanager_name

1*

Private_shareholder_type

private_shareholder_type {id}

1

**

*

1

1Shareholder_type


Shareholder

shareholder_name{id}public_shareholder_levelmanager_name

1*

Private_shareholder_type

private_shareholder_type {id}

1

**

*

1

1

Occurrences of shareholder_type: {private,public,both}Occurrences of private_shareholder_type: {person,company,others}


Logical designLogical design From enriched/transformed UML model to unified From enriched/transformed UML model to unified

multidimensional model. Mapping of:multidimensional model. Mapping of: Ordinary classes and their attributes (transformations Tcl1 to Tcl3)Ordinary classes and their attributes (transformations Tcl1 to Tcl3) Associations and their attributes (transformations Tcl4 to Tcl6).Associations and their attributes (transformations Tcl4 to Tcl6).

Mapping ordinary classes and their attributes :Mapping ordinary classes and their attributes : Transformation Tcl1: The identifying attribute of each ordinary class is Transformation Tcl1: The identifying attribute of each ordinary class is

mapped into a dimension in the multidimensional model. mapped into a dimension in the multidimensional model. Transformation Tcl2: The non-identifying attributes of each ordinary Transformation Tcl2: The non-identifying attributes of each ordinary

class are mapped into dimension attributes in the multidimensional model class are mapped into dimension attributes in the multidimensional model if these non-identifying attributes are not measures of interest. if these non-identifying attributes are not measures of interest.

Transformation Tcl3: The non-identifying attributes of each ordinary Transformation Tcl3: The non-identifying attributes of each ordinary class are mapped into measures in the multidimensional model if these class are mapped into measures in the multidimensional model if these non-identifying attributes are measures of interest. non-identifying attributes are measures of interest.

3. Design method


Logical designLogical design Specifying transformation Tcl3 with OCL :Specifying transformation Tcl3 with OCL :

ContextContext UMLModel::Tcl3(nonIdentifier:Attribute, UMLModel::Tcl3(nonIdentifier:Attribute,multidimensionalModel:MultidimensionalModel)multidimensionalModel:MultidimensionalModel):Measure:Measureprepre: nonIdentifier.owner.oclIsTypeOf(OrdinaryClass): nonIdentifier.owner.oclIsTypeOf(OrdinaryClass)

=true=true andand nonIdentifier.identifyingAttribute=falsenonIdentifier.identifyingAttribute=false andand nonIdentifier.measure=truenonIdentifier.measure=truepostpost:result.name=nonIdentifier.name:result.name=nonIdentifier.namepost:post:nonIdentifier.owner.attribute->nonIdentifier.owner.attribute->

forall(a1:Attribute|forall(a1:Attribute| ifif a1.identifyingAttribute=true a1.identifyingAttribute=true thenthen result.dimension=Tcl1(a1) result.dimension=Tcl1(a1) endifendif))postpost:multimensionalModel->includes(result) :multimensionalModel->includes(result)

3. Design method


Logical designLogical design Mapping ordinary classes and their attributes (example):Mapping ordinary classes and their attributes (example):

3. Design method

dimension target_codedimension quarterdimension year dimension regiondimension media_namedimension media_type

attribute status [target_code]attribute minimum_age [target_code]attribute maximum_age [target_code]attribute sex [target_code]attribute insertion [media_type]attribute advertising_price [media_name]

measure percentage_of_region [target_code]measure number_of_inhabitants [region]

exposure

media_exposure {meas}

Media_type

media_type {id}insertion

Region

region {id}number_of_inhabitants {meas}

Media

media_name {id}advertising _price

1

*

1

**

1..*

*

1..*gets

Target

target_code {id}statusminimum_agemaximum_agesexpercentage_of_region {meas}

*

*

*

*

*

exposure


Media_type


Region


Year

year {id}

Quarter

quarter {id}

1

1..*

1

1..*

Year

year {id}

Quarter

quarter {id}

1

1..*

1

1..*

Media


1

*

1

**

1..*

*

1..*gets

Target


*

*

*

*

*

Enriched/transformed UML model


Transformation Tcl1

Transformation Tcl2

Transformation Tcl3


Logical designLogical design Mapping associations and their attributes :Mapping associations and their attributes :

Transformation Tcl4: The attributes of each association class Transformation Tcl4: The attributes of each association class are mapped into measures, associated with dimensions are mapped into measures, associated with dimensions obtained by mapping the identifying attributes of the ordinary obtained by mapping the identifying attributes of the ordinary classes directly or indirectly participating in the association classes directly or indirectly participating in the association class (transformation Tcl1). class (transformation Tcl1).

Transformation Tcl5: A path formed by N-1 associations is Transformation Tcl5: A path formed by N-1 associations is mapped into a hierarchy in the multidimensional model. mapped into a hierarchy in the multidimensional model.

Transformation Tcl6: Every N-M or N-ary association Transformation Tcl6: Every N-M or N-ary association without at least one attribute that is always defined is mapped without at least one attribute that is always defined is mapped into a dummy measure, associated with dimensions obtained into a dummy measure, associated with dimensions obtained by mapping the identifying attributes of the ordinary classes by mapping the identifying attributes of the ordinary classes directly or indirectly participating in the association directly or indirectly participating in the association (transformation Tcl1). (transformation Tcl1).

3. Design method


Logical designLogical design Mapping Mapping associationsassociations and their attributes (example): and their attributes (example):

3. Design method

dimension target_codedimension quarterdimension year dimension regiondimension media_namedimension media_type

attribute status [target_code]attribute minimum_age [target_code]attribute maximum_age [target_code]attribute sex [target_code]attribute insertion [media_type]attribute advertising_price [media_name]

measure percentage_of_region [target_code]measure number_of_inhabitants [region]

measure media_exposure [media_name,target_code,quarter]

hierarchy time quarter->year hierarchy media_type media_name->media_type

dummy measure gets [region,media_name]

exposure


Media_type


Region


Media


1

*

1

**

1..*

*

1..*gets

Target


*

*

*

*

*

exposure


Media_type


Region


Year

year {id}

Quarter

quarter {id}

1..*

Year

year {id}

Quarter

quarter {id}

Media


1

*

1

*1..*

Target


*

*

*

*

*

Enriched/transformed UML model


Transformation Tcl4

Transformation Tcl5

Transformation Tcl6

1


Physical designPhysical design For each type of target system: metamodel + associated For each type of target system: metamodel + associated

transformations (elaborates on/completes OMG’s transformations (elaborates on/completes OMG’s Common Warehouse Metamodel).Common Warehouse Metamodel).

Example transformation (ROLAP star) :Example transformation (ROLAP star) : Transformation Tls4: Every hierarchy D1->D2->…->Dn of Transformation Tls4: Every hierarchy D1->D2->…->Dn of

the logical model is mapped by considering all the sub-the logical model is mapped by considering all the sub-hierarchies Dj->Dj+1…->Dn where 1<=j<n and Dj hierarchies Dj->Dj+1…->Dn where 1<=j<n and Dj dimensions at least one measure. A sub-hierarchy Dj-dimensions at least one measure. A sub-hierarchy Dj->Dj+1…->Dn is mapped in the physical model by defining in >Dj+1…->Dn is mapped in the physical model by defining in the dimension table identified by Dj a column corresponding the dimension table identified by Dj a column corresponding to each of the Di (where j<i<=n). to each of the Di (where j<i<=n).

3. Design method


ConclusionConclusion Data warehouse design method based on UML:Data warehouse design method based on UML:

Spans the conceptual/logical/physical levelsSpans the conceptual/logical/physical levels Each step: metamodels + associated transformationsEach step: metamodels + associated transformations Unified multidimensional Unified multidimensional metametamodel at the logical level model at the logical level

((pivot metamodelpivot metamodel).).

Tool support (prototype developed).Tool support (prototype developed).

Future works:Future works: Complete/specialise set of transformationsComplete/specialise set of transformations Further experimentationFurther experimentation Reverse engineering.Reverse engineering.

4. Conclusion

from uml to rolap multidimensional databases using a pivot model

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