Public:BWmeta service/Transformers

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Service details
Name	BWmeta
Code location (relative to SVN root)	projects/dir/bwmeta-core
Javadoc
Contact person	Jakub Jurkiewicz
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Contents 1 Background and motivation 2 Unified interface 3 Existing transformers in YADDA 4 MetadataTransformerFactory 5 MetadataTransformerFactory in YADDA 6 Description of transformers interface 7 Description of MetadataTransformerFactory interface

Background and motivation

As of 2010Q4, three versions of BWmeta format and at least three Java models of BWmeta are used in YADDA. See here for details. Serialization and deserialization is implemented for the following pairs:

	Repo	DL	Y	…
1.0.5
1.2.0
2.0.0

There are also converters between selected models:

• Y ↔ DL

Serialization of Y model to BWmeta 1.0.5 is therefore possible through the following chain of transformations:

• Y model → DL model → BWmeta 1.0.5

Conversion from DL model to Repo model is possible through:

• DL model → BWmeta 1.0.5 → Repo model

Unfortunately, many mutually-incompatible transformation interfaces are present. It is difficult to understand which transformations are possible, how to combine them, which classes should be used for that end and how to instantiate the classes.

A unified interface to all the transformations would be very helpful.

Unified interface

Four different transformer types are present: readers, writers and model converters and format converters. Each type has a corresponding interface:

• IMetadataReader<T> deserializes an object of type T from a String or a Reader
• IMetadataWriter<T> serializes an object of type T to a String or a Writer
• IMetadataModelConverter<S, T> converts an object of type S to an object of type T
• IMetadataFormatConverter converts serialized metadata from one format to another one

See detailed description of transformers interface below.

Existing transformers in YADDA

Existing transformers are located in the pl.edu.icm.yadda.bwmeta.transformers package.

Readers:

Class name	Format	Model
Bwmeta1_0ToDLTransformer	BWmeta 1.0	DL
Bwmeta1_0ToRepoTransformer	BWmeta 1.0	Repo
Bwmeta1_2ToYTransformer	BWmeta 1.2	Y
Bwmeta2_0ToYTransfomrer	BWmeta 2.0	Y

Writers:

Class name	Model	Format
DLToBwmeta1_0Transformer	DL	BWmeta 1.0
RepoToBwmeta1_0Transformer	Repo	BWmeta 1.0
YToBwmeta1_2Transformer	Y	BWmeta 1.2
YToBwmeta2_0Transformer	Y	BWmeta 2.0

Model converters:

Class name	Source model	Target model
DLToYTransformer	DL	Y
YToDLTransformer	Y	DL

MetadataTransformerFactory

MetadataTransformerFactory maintains a list of available "atomic" transformers and is able to combine the atomic transformers into more complex ones.

MetadataTransformerFactory in YADDA

There is a static instantion of MetadataTransformerFactory pl.edu.icm.yadda.bwmeta.transformers.BwmetaTransformers.BTF, which can be used in many typical situations. New transformers should be added to this factory.

See detailed description of MetadataTransformerFactory below.

Description of transformers interface

Classes listed in Unified interface section provide following methods:

IMetadataReader<T> (T is a model class)

• MetadataFormat getSourceFormat() -- return the source format
• MetadataModel<T> getTargetModel() -- returns the target model
• List<T> read(String string, Object... hints) throws TransformationException -- deserializes metadata from string; returns a list of model objects.
• List<T> read(Reader reader, Object... hints) throws TransformationException -- deserializes metadata from reader stream; returns a list of model objects.

IMetadataWriter<T>

• MetadataModel<T> getSourceModel() -- returns the source model
• MetadataFormat getTargetFormat() -- returns the target format
• String write(List<T> objects, Object... hints) throws TransformationException -- serializes metadata model objects given in objects list; returns a string contains all metadata
• void write(Writer writer, List<T> objects, Object... hints) throws TransformationException -- serializes metadata model objects given in objects list; the result is written into writer stream.

IMetadataModelConverter<S, T>

• MetadataModel<S> getSourceModel() -- returns the source model
• MetadataModel<T> -- returns the target model
• T convert(S source, Object... hints) throws TransformationException; -- converts a metadata object of type S into objects of type T

IMetadataFormatConverter

• MetadataFormat getSourceFormat() -- returns the source format
• MetadataFormat getTargetFormat() -- returns the target format
• String convert(String source, Object... hints) throws TransformationException -- converts serialized metadata given in source string; returns a string containing metadata in target format
• void convert(Reader from, Writer to, Object... hints) throws TransformationException -- converts serialized metadata read from a stream from; metadata in target format are written into a to stream.

Description of MetadataTransformerFactory interface

Public constructors provided by MetadataTransformerFactory:

• MetadataTransformerFactory(List<IMetadataReaders>, List<IMetadataWriters>, List<IMetadataModelConverters>, List<IMetadataFormatConverters>) -- builds a MetadataTransformerFactory from given lists of atomic transformers,
• MetadataTransformerFactory(MetadataTransformerFactory, List<IMetadataReaders>, List<IMetadataWriters>, List<IMetadataModelConverters>, List<IMetadataFormatConverters>) -- creates a new MetadataTransformerFactory from an existing one, which contains joined lists of atomic transformers.

Public methods of MetadataTransformerFactory, that return return transformer built from atomic transformers given in object constructor:

• <T> IMetadataReader<T> getReader(MetadataModel<T>, MetadataFormat)
• <T> IMetadataWriter<T> getWriter(MetadataModel<T>, MetadataFormat)
• <S, T> IMetadataModelConverter<S, T> getModelConverter(MetadataModel<S>, MetadataModel<T>)
• IMetadataFormatConverter getFormatConverter(MetadataFormat, MetadataFormat)

MetadataTransformerFactory also contains a set of static methods compose(), that return a complex transformer built from two given transformers. These methods are not part of IMetadataTransformerFactory interface.

• IMetadataReader compose(IMetadataFormatConverter, IMetadataReader)
• IMetadataReader compose(IMetadataReader, IMetadataModelConverter)
• IMetadataWriter compose(IMetadataWriter, IMetadataFormatConverter)
• IMetadataWriter compose(IMetadataModelConverter, IMetadataWriter)
• IMetadataFormatConverter compose(IMetadataFormatConverter, IMetadataFormatConverter)
• IMetadataFormatConverter compose(IMetadataReader, IMetadataWriter)
• IMetadataModelConverter compose(IMetadataModelConverter, IMetadataModelConverter)
• IMetadataModelConverter compose(IMetadataWriter, IMetadataReader)