Lesson7WebML.pdf

Advanced Software Engineering
Paolo Bottoni
Lecture 7: WebML (IFML)

IFML usage
• High-level description of a Web application
• Multiple views of the same content
• Repository of the meta-information collected during
the design process
• Data manipulation operations for
– updating the site content
– interacting with arbitrary external services
• Separate information content from composition into
pages, navigation, and presentation
• Explicit modelling of users and communities
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Advanced Software Engineering Lesson7WebML

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What it is for:
interaction
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4
What it is for: multiple
interaction
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What it is for:
actions
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What it is for: forms
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The IFML metamodel

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Metamodel for interaction flow

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Metamodel for events

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Metamodel for parameter binding

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Metamodel for view components

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Metamodel for modules

Models
• Data Model
– conceptual data organization
– compatible with ER and UML class diagrams.
• Derivation model
– extends structure model with calculated data
• Hypertext model
– specification of the front-end of the application
• Content Management Model
– extends hypertext model with operations and transactions
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Data Model
• Based on Entity-Relationship
– Entities, attributes, data types, relationships
• Entities
– Description of common features of set of objects
– Population: set of objects described by entity.
• Attributes
– relevant properties of real world objects
– entity instances characterized by same attributes
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Relationships
• Generalization
– Single inheritance among entities
– Instances from only one sub-entity
– Entities in at most one generalization hierarchy
• Relations
– Semantic connections between entities
– Entities have roles
– Minimum and maximum cardinality constraints
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Notations
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Derivation model
• Extends the elements of the structure model with
calculated elements
– Augment entity content by adding attributes calculated
or imported from related objects
– Define populations of entities and relationships based
on some property of the involved objects
• WebML-OQL: set-oriented, navigational query
language
– Now the standard defines only the metamodel
• UML OCL and OQL path expressions
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WEBML-OQL attributes
• Imported
– affiliationName = Self.Affiliation.name
• Calculated
– netPrice = Self.grossPrice – Self.tax
• Aggregate
– totalAlbums = count(Self.ArtistToAlbum)
– TotalTracksDuration =
sum(Self.ArtistToAlbum.AlbumToTrack.duration)
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WEBML-OQL filters
recentAlbumsCount =
count(Self.ArtistToAlbum as B
WHERE B.date > '1997-01-01')
totRecentTracksDuration =
sum(Self.ArtistToAlbum(as B).
AlbumToTrack.duration
WHERE B.date > '1997-01-01').
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WebML-OQL: derived relationships
• Concatenation of relationships
CoParticipation =
Self.ArtistToCompilation.CompilationToArtist
• Evaluation of predicates
CoParticipation = Self.ArtistToCompilation.CompilationToArtist
as A where Self.Affiliation = A.Affiliation
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Hypertext model
• Specifies organization of front-end interfaces
• Elements:
– units: atomic pieces of publishable content
– pages: interface elements delivered to users
– links: navigation and parameter passing
• Modularization constructs
– areas: clusters of pages with homogeneous purpose
– site view: coherent hypertext for set of requirements
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Units
• Data unit: information about single object.
• Multidata unit: information about set of objects
• Index unit: list of descriptive properties of objects.
• Scroller unit: browsing of ordered set
• Entry unit: entry forms for input gathering.
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Icons for units (WebML)
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From WebML to IFML I

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From WebML to IFML II

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From WebML to IFML III
Module
Parameter Binding

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Architecture of IFML diagrams

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Diagram interchange metamodel

Role of units
Multiplicity Role Operations
Data Single Presentation Publishing
Set Presentation Publishing
Index Set Selection Publishing
Set Selection Publishing
Entry Acquisition
Multidata
Scroller
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Getting content for data units
• Source: name of entity, type of object
providing content.
• Selector: predicate to determine the actual
objects of the source entity that contribute
– Conjunction / Disjunction of elementary
conditions, built from entity attributes and relations
and from constant or variable terms.
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Getting content for multidata units
• Name: user-defined name
• Source: entity providing content
• Selector: predicate selecting objects.
• Included attributes: set of attributes to be
visualized for each object
• Order clause: set of attributes used to sort
objects and sorting criterion
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Getting content for index units
• Selector: predicate selecting objects
• Included attributes: set of attributes used to display the index entries.
• Order clause: set of attributes used to sort objects and sorting criterion
• Variants:
– multi-choice index unit, checkbox associated with entries
– hierarchical index, index entries organised in a multi-level tree
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Notation
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Variants of index units
IndexUnit AlbumIndex hierarchical
(source Album;
attributes Title;
orderby Title
NEST Track
selector AlbumToTrack;
attributes Title;
orderby Title)
IndexUnit AlbumIndex multi-choice
(source Album;
attributes Title;
orderby Title)
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Scroller units
• Selector: predicate selecting objects
• Block factor: number of objects scrolled together.
• Block window: maximum number of shown blocks
that preceed and follow the current block
• Order clause:set of attributes used to sort the objects
and sorting criterion
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Entry units
• Fields: set of fields for inputting values.
• Property of fields:
– Name: name of the field.
– Type: data type of the value input
– Initial value: default value initially proposed
– Modifiability: flag specifying if the user can modify the initial
field value or not
– Validity predicate: Boolean condition on the input
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Notation
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Links
Inter-Page
Contextual CA CE
Non contextual NA NE
Intra-Page
parametric selector
link parameter
NE
CE
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Links
CA
Multiple outgoing links from a hierarchy
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Complex navigations
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Global parameters
• Context information not transferred point-to-
point during navigation, but available to all
the pages of a site
– e.g. multi-country Web site, user selects the
country of interest and then browses the site's
content relative to that country
– hypertext the same for all countries, actual content
varies country by country
• Use of set unit
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Views and areas
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Conjunctive nested pages
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Disjunctive nested pages
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Content management model
• Operation unit: processing executed as result of link
navigation
– data manipulation
– execution of a generic external service.
• OK and KO-links: operation success and failure
– allow alternative courses after execution of an operation
• Transactions: clusters of operation units
– succeed or fail as a whole. Undone if one fails
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Operations
• Predefined
– Creation, deletion and modification of objects, and relationships.
• Generic
– Integration of external procedures of arbitrary complexity
• Operations:
– May have multiple incoming links.
– May be linked to form a sequence.
– One regular incoming link, and transport links. Navigates the
regular link and uses the parameters associated with input links.
– Have one OK link and one KO link
– May have any number of outgoing transport links
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Icons for operations
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Object creation
User-defined Name
Source entity
Set of assignments
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Object deletion
User-defined name
Source entity
Selector
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Multiple deletion
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Object modification
User-defined name
Source entity
Selector
Set of assignments
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Relation creation
User-defined name
Source relationship role
Two selectors, one for
objects of the source entity
and one for objects of the
destination entity.
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Relation deletion
User-defined name
Source relationship role
Two selectors, one for
objects of the source
entity and one for object
of the destination entity.
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Transactions
• ACID properties
– Atomicity: either all the involved operations are successfully
completed, producing a new database state, or the initial
database state is left unchanged.
– Consistency: carrying out a transaction should not violate the
integrity of data.
– Isolation: each transaction execution is independent of the
simultaneous execution of other transactions.
– Durability: effects of transactions that complete successfully are
recorded persistently.
• Operations chained by a sequence of OK links
• The last OK link leads to the (unique) hypertext page shown
after the successful completion of the transaction.
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Icons for sessions
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Icons for services
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Icons for control flow
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Icons for utilities
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Lesson7WebML.pdf

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