Digital Libraries of the Future Use of Semantic Web and Social Bookmarking to support E-learning in Digital Libraries Sebastian Ryszard Kruk Digital Enterprise Research Institute National University of Ireland, Galway sebastian.kruk @deri.org http:// corrib.deri.ie /

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

Motivations John teaches biology, over the Internet, using digital libraries and modern technologies (wikis, blogs) How to deliver the material just-in-time? How to pre-asses students? How to automate most of the process?

John teaches biology, over the Internet, using digital libraries and modern technologies (wikis, blogs)

How to deliver the material just-in-time?

How to pre-asses students?

How to automate most of the process?

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

The Semantic Web – Applications Semantic Web cannot be and is not only a set of recommendations Semantic Web is becoming reality by applications that support it and are based on it Enabling technologies: RDF Storages: Sesame, Jena, YARS Reasoners: KAON, Racer Editors: Protege, SWOOP, MarcOnt Portal End-User applications: Semantic wikis: Makna, SemperWiki Semantic blogs Semantic digital libraries

Semantic Web cannot be and is not only a set of recommendations

Semantic Web is becoming reality by applications that support it and are based on it

Enabling technologies:

RDF Storages: Sesame, Jena, YARS

Reasoners: KAON, Racer

Editors: Protege, SWOOP, MarcOnt Portal

End-User applications:

Semantic wikis: Makna, SemperWiki

Semantic blogs

Semantic digital libraries

What is a Semantic Digital Library? Semantic digital libraries integrate information based on different metadata, e.g.: resources, user profiles, bookmarks, taxonomies – high quality semantics = highly and meaningfully connected information provide interoperability with other systems (not only digital libraries) on either metadata or communication level or both – RDF as common denominator between digital libraries and other services delivering more robust, user friendly and adaptable search and browsing interfaces empowered by semantics

Semantic digital libraries

integrate information based on different metadata, e.g.: resources, user profiles, bookmarks, taxonomies – high quality semantics = highly and meaningfully connected information

provide interoperability with other systems (not only digital libraries) on either metadata or communication level or both – RDF as common denominator between digital libraries and other services

delivering more robust, user friendly and adaptable search and browsing interfaces empowered by semantics

Semantic Web Technologies for Digital Libraries? Metadata is the key concept the Web does not have metadata the idea of a Semantic Web is nice but difficult to implement many digital libraries do have metadata in place we simply must make them available in a machine understandable format the Semantic Web provides the format: RDF

Metadata is the key concept

the Web does not have metadata

the idea of a Semantic Web is nice but difficult to implement

many digital libraries do have metadata in place

we simply must make them available in a machine understandable format

the Semantic Web provides the format: RDF

Semantic Web Technologies for Digital Libraries? Knowledge in bibliographic records Digital Libraries already have controlled vocabularies, taxonomies or even ontologies in place the challenge is to model this knowledge in a machine understandable way the Semantic Web provides ontology languages: RDF Schema OWL SKOS

Knowledge in bibliographic records

Digital Libraries already have controlled vocabularies, taxonomies or even ontologies in place

the challenge is to model this knowledge in a machine understandable way

the Semantic Web provides ontology languages:

RDF Schema

OWL

SKOS

Taxonomy of Knowledge Organization Systems Term Lists Authority files ( FOAF ) Glossaries Dictionaries Gazetteers Classifications and Categories ( DMoz ) Subject headings Classification schemes Taxonomies Categorization Schemes. Relationship Lists Thesauri ( WordNet, MeSH ) Semantic networks Ontologies (Hodge, 2000)

Term Lists

Authority files ( FOAF )

Glossaries

Dictionaries

Gazetteers

Classifications and Categories ( DMoz )

Subject headings

Classification schemes

Taxonomies

Categorization Schemes.

Relationship Lists

Thesauri ( WordNet, MeSH )

Semantic networks

Ontologies

Benefits of Semantic Digital Libraries The two main benefits of Semantic Digital Libraries new search paradigms for the information space Ontology-based search / facet search Community-enabled browsing providing interoperability on the data level integrating metadata from various heterogeneous sources Interconnecting different digital library systems

The two main benefits of Semantic Digital Libraries

new search paradigms for the information space

Ontology-based search / facet search

Community-enabled browsing

providing interoperability on the data level

integrating metadata from various heterogeneous sources

Interconnecting different digital library systems

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

Semantic DL as Evolving Knowledge Space In state-of-the-art digital libraries users are consumers Retrieve contents based on available bibliographic records Recent trends: user communities Connetea Flickr In Semantic digital libraries users are contributers as well Tagging (Web 2.0) Social Semantic Collaborative Filtering Annotations Semantic Digital libraries enforce the transition from a static information to a dynamic (collaborative) knowledge space

In state-of-the-art digital libraries users are consumers

Retrieve contents based on available bibliographic records

Recent trends: user communities

Connetea

Flickr

In Semantic digital libraries users are contributers as well

Tagging (Web 2.0)

Social Semantic Collaborative Filtering

Annotations

Semantic Digital libraries enforce the transition from a static information to a dynamic (collaborative) knowledge space

Why current (semantic) digital libraries are not enough? digital libraries should not be for librarians only but for average people they concentrate on delivering content/information, not on knowledge sharing within a community of users digital libraries have lost human-part of their predecessors What could be the solution? make users/readers involved in the content annotation process allow users/readers to share their knowledge within a community provide better communication between users in and across communities The future - Social Semantic Digital Libraries

Why current (semantic) digital libraries are not enough?

digital libraries should not be for librarians only but for average people

they concentrate on delivering content/information, not on knowledge sharing within a community of users

digital libraries have lost human-part of their predecessors

What could be the solution?

make users/readers involved in the content annotation process

allow users/readers to share their knowledge within a community

provide better communication between users in and across communities

Social Semantic Information Spaces

Comparing Web 1.0 / Web 2.0 / Semantic Web 2.0 Semantic Social Networks Online Social Networks Buddy Lists, Address Books Semantic Social Information Spaces - - Social Semantic Digital Libraries Google Scholar, Book Search CiteSeer, Project Gutenberg Semantic Forums and Community Portals Community Portals Message Boards Semantic Blogs Blogs Personal Websites Semantic Search Google Personalised, DumbFind Altavista, Google Semantic Wikis Wikis Content Management Systems Semantic Web 2.0 Web 2.0 Web 1.0

Evolution of Libraries Social Semantic Digital Library Involves the community into sharing knowledge Semantic Digital Library Accessible by machines, not only with machines Digital Library Online, easy searching with a full-text index Library Organized collection

Existing Semantic Digital Library Systems SIMILE extends and laverages DSpace, seeking to enhance interoperability among digital assets, schemata, metadata, and services JeromeDL a social semantic digital library makes use of Semantic Web and Social Networking technologies to enhance both interoperability and usability BRICKS aims at establishing the organizational and technological foundations for a digital library network in order to share knowledge and resources in the cultural heritage domain. FEDORA delivers flexible service-oriented architecture to managing and delivering content in the form of digital objects

SIMILE

extends and laverages DSpace, seeking to enhance interoperability among digital assets, schemata, metadata, and services

JeromeDL

a social semantic digital library makes use of Semantic Web and Social Networking technologies to enhance both interoperability and usability

BRICKS

aims at establishing the organizational and technological foundations for a digital library network in order to share knowledge and resources in the cultural heritage domain.

FEDORA

delivers flexible service-oriented architecture to managing and delivering content in the form of digital objects

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

JeromeDL - Introduction Joint effort of DERI, National University of Ireland, Galway and Gdansk University of Technology (GUT) Distributed under BSD Open Source license Digital library build on semantic web technologies to answer requirements from: librarians, scientists and everyone.

Joint effort of DERI, National University of Ireland, Galway and Gdansk University of Technology (GUT)

Distributed under BSD Open Source license

Digital library build on semantic web technologies to answer requirements from: librarians, scientists and everyone.

JeromeDL – Motivations Use Cases Librarians: support for rich metadata (MARC21) in uploading resources, accessing bibliographic information and searching persistent identifiers Scientists: easy publishing (designed as a institute/university digital library) creating hierarchical networks of digital libraries support for accessing, sharing and searching using bibliography metadata (BibTeX) Everyone: simple search (incl. natural language queries) community-aware information sharing and browsing, support for interationalization

Librarians:

support for rich metadata (MARC21) in uploading resources, accessing bibliographic information and searching

persistent identifiers

Scientists:

easy publishing (designed as a institute/university digital library)

creating hierarchical networks of digital libraries

support for accessing, sharing and searching using bibliography metadata (BibTeX)

Everyone:

simple search (incl. natural language queries)

community-aware information sharing and browsing,

support for interationalization

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

JeromeDL – Architecture Resources and annotations repository Middleware: query processing community space resources management User interface agents: Communication to the outside world Administrative interface

Resources and annotations repository

Middleware:

query processing

community space

resources management

User interface agents:

Communication to the outside world

Administrative interface

Structure ontology in JeromeDL

Bibliographic (MarcOnt) Ontology in JeromeDL

Community-aware (FOAFRealm) ontology

Ontologies in JeromeDL

Metadata and Services in JeromeDL

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

MarcOnt Initiative – Overview Motivation: Provide set of tools for collaborative ontology development MarcOnt Initiative goals: Create a framework for collaborative ontology improvement (E-learning) Provide domain experts with tools to share their knowledge Offer tools for data mediation between different data formats

Motivation:

Provide set of tools for

collaborative ontology

development

MarcOnt Initiative goals:

Create a framework for collaborative ontology improvement (E-learning)

Provide domain experts with tools to share their knowledge

Offer tools for data mediation between different data formats

MarcOnt Portal and MarcOnt Ontology MarcOnt Ontology: Central point of MarcOnt Initiative Translation and mediation format Continuos collaborative ontology improvement Knowledge from the domain experts MarcOnt Portal (source of knowledge): Suggestions Annotations Versioning Ontology editor

MarcOnt Ontology:

Central point of MarcOnt Initiative

Translation and mediation format

Continuos collaborative ontology improvement

Knowledge from the domain experts

MarcOnt Portal (source of knowledge):

Suggestions

Annotations

Versioning

Ontology editor

MarcOnt Mediation Services for Legacy Metadata Format translation RDF Translator Format co-operation MarcOnt Mediation Services

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

Social Services in JeromeDL Involve users into sharing knowledge Blogs – comments and discussions about documents and resources Tagging – collaborative classification Wikis – collaboratively edited additional descriptions , such as summaries and interesting facts Preserve knowledge for future use Users can learn from experience of others instantly Recommend new, interesting resources based on users’ profiles

Involve users into sharing knowledge

Blogs – comments and discussions about documents and resources

Tagging – collaborative classification

Wikis – collaboratively edited additional descriptions , such as summaries and interesting facts

Preserve knowledge for future use

Users can learn from experience of others instantly

Recommend new, interesting resources based on users’ profiles

Identity management with FOAFRealm Identity defined with extended FOAF metadata Policies expressed by social networking Distance between owner and requester Friendship level between owner and requester, calculated across digraph of social network Support for single registration and sign on Distributed identity management with HyperCuP (“D-FOAF”) FOAFRealm is currently implemented as a plugin for Tomcat (Realm/Valve implementation), with PHP and .NET versions coming soon

Identity defined with extended FOAF metadata

Policies expressed by social networking

Distance between owner and requester

Friendship level between owner and requester, calculated across digraph of social network

Support for single registration and sign on

Distributed identity management with HyperCuP (“D-FOAF”)

FOAFRealm is currently implemented as a plugin for Tomcat (Realm/Valve implementation), with PHP and .NET versions coming soon

What is S ocial S emantic C ollaborative F iltering? Goal: t o enhance individual bookmarks with shared knowledge within a community Users annotate catalogues of bookmarks with semantic information taken from DM oz or WordNet vocabularies Catalogs can include ( transclusion ) friend's catalogues Access to catalogues can be restricted with social networking-based polices SSCF delivers: Community-oriented, semantically-rich taxonomies Information about a user's interest Flows of expertise from the domain expert Recommendations based on users previous actions Support for SIOC metadata

Goal: t o enhance individual bookmarks with shared knowledge within a community

Users annotate catalogues of bookmarks with semantic information taken from DM oz or WordNet vocabularies

Catalogs can include ( transclusion ) friend's catalogues

Access to catalogues can be restricted with social networking-based polices

SSCF delivers:

Community-oriented, semantically-rich taxonomies

Information about a user's interest

Flows of expertise from the domain expert

Recommendations based on users previous actions

Support for SIOC metadata

Example of S ocial S emantic C ollaborative F iltering foaf:knows xfoaf:include xfoaf:bookmark

Social Networks in Digital Libraries Resource xfoaf:Annotation user_C creator_B foaf:knows marcont:hasCreator creator_A foaf:knows foaf:knows xfoaf:Directory user_D xfoaf:owns xfoaf:linksTo xfoaf:isIn

Support for online communities in SSCF

Support for online communities in SSCF

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

JeromeDL – Delivering Semantic Content Providing semantic annotations during uploading process : open module for handling any taxonomies keywords based on WordNet and free tagging defining structure of resources in the JeromeDL ontology Lifting legacy metadata to MarcOnt ontology Community maintained annotations social semantic collaborative filtering semantic descriptions based on the FOAF metadata

Providing semantic annotations during uploading process :

open module for handling any taxonomies

keywords based on WordNet and free tagging

defining structure of resources in the JeromeDL ontology

Lifting legacy metadata to MarcOnt ontology

Community maintained annotations

social semantic collaborative filtering

semantic descriptions based on the FOAF metadata

Annotating Library Resources

JeromeDL – Semantic Information In Use Searching: Keyword-based search with semantic query expansion Semantic search: Direct RDF quering Natural language templates Browsing Exibit MultiBeeBrowse Sharing: Social Semantic Collaborative Filtering Semantically Interlinked Online Communities Heterogeneous communication: Bibster , A9 , OAI -PMH

Searching:

Keyword-based search with semantic query expansion

Semantic search:

Direct RDF quering

Natural language templates

Browsing

Exibit

MultiBeeBrowse

Sharing:

Social Semantic Collaborative Filtering

Semantically Interlinked Online Communities

Heterogeneous communication:

Bibster , A9 , OAI -PMH

Exposing Semantic Annotations

Filtering Resources in JeromeDL

Sharing Knowledge with SSCF

Information Retrieval in JeromeDL Fulltext Index Structure Repository MarcOnt Repository Resources’ Content FOAFRealm Repository (typed) keywords RDF & NL Query OpenSearch RSS collaborative filtering types translation semantic query expansion RDF Repositories Secure Snapshot local interface distributed interface

Networks of Digital Libraries ELP (Extensible Library Protocol) implementation communication within JeromeDL network adapters for communication with other networks D-FOAF integration (distributed user profile management) single sign on and single registration within D-FOAF network HyperCuP integration (scalable P2P network) Independent ELP network entry point: http://search.jeromedl.org/ 0 0 1 1 0 0 1 1 0 2 2 2 2

ELP (Extensible Library Protocol) implementation

communication within JeromeDL network

adapters for communication with other networks

D-FOAF integration (distributed user profile management)

single sign on and single registration within D-FOAF network

HyperCuP integration (scalable P2P network)

Independent ELP network entry point: http://search.jeromedl.org/

JeromeDL in Action

Presentation outline Motivation Building Social Semantic Digital Library Semantic Digital Libraries Towards Online Communities for Digital Libraries JeromeDL and other Corrib components Motivation and Overview Architecture and Ontologies Semantic Services Social Services Semantics in Use JeromeDL in Action e-Learning 2.0 Conclusions

Motivation

Building Social Semantic Digital Library

Semantic Digital Libraries

Towards Online Communities for Digital Libraries

JeromeDL and other Corrib components

Motivation and Overview

Architecture and Ontologies

Semantic Services

Social Services

Semantics in Use

JeromeDL in Action

e-Learning 2.0

Conclusions

Web 1.0 e-Learning Creation Consumption

Web 2.0 e-Learning Creation Communities Consumption

Semantic Web e-Learning Semantic sources Creation Consumption

Semantic Web 2.0 e-Learning Contribution Creation Consumption Communities Semantic sources

Didaskon project Deliver a framework for assemblying an on-demand curriculum from existing Learning Objects (LOs) provided by e-Learning services Connection between formal and informal learning : Repository of couses prepared by specialists (formal LOs) Transform data collected from SSIS into LOs (informal knowledge) – IKHarvester Used o ntolog ies link user needs and the characteristics of the learning material

Deliver a framework for assemblying an on-demand curriculum from existing Learning Objects (LOs) provided by e-Learning services

Connection between formal and informal learning :

Repository of couses prepared by specialists (formal LOs)

Transform data collected from SSIS into LOs (informal knowledge) – IKHarvester

Used o ntolog ies link user needs and the characteristics of the learning material

Didaskon project LOs described with LOM ontology, composed into a learning path for a specific student User profile (knowledge level in different domains and goals/expectations from the course) described with FOAF ontology – preconditions Didaskon: returns learning material customized for specific user’s needs allows more scalable helper features for students supervision Produced curriculum: reflects user requirements introduces new interdisciplinary, extensible and robust meaning of e-Learning

LOs described with LOM ontology, composed into a learning path for a specific student

User profile (knowledge level in different domains and goals/expectations from the course) described with FOAF ontology – preconditions

Didaskon:

returns learning material customized for specific user’s needs

allows more scalable helper features for students supervision

Produced curriculum:

reflects user requirements

introduces new interdisciplinary, extensible and robust meaning of e-Learning

One of potential sources of future e-Learning systems On the verge between formal (libraries) and informal (communities) learning sources Semantic interoperability with Learning Management Systems Improve knowledge creation, delivery and sharing E-Learning Solution based on Social Sem. DL

One of potential sources of future e-Learning systems

On the verge between formal (libraries) and informal (communities) learning sources

Semantic interoperability with Learning Management Systems

Improve knowledge creation, delivery and sharing

E-Learning Solution based on Social Sem. DL

Comparison between process based on JeromeDL and a set of other services Some tasks take shorter to execute with JeromeDL Some tasks are automated within JeromeDL Roughly twice less time spend with JeromeDL Evaluation of e-Learning Solution based on SSDL

Comparison between process based on JeromeDL and a set of other services

Some tasks take shorter to execute with JeromeDL

Some tasks are automated within JeromeDL

Roughly twice less time spend with JeromeDL

E-Learning Project at DERI Galway

Between e-Learning and DL - Museum Scenario Museums have physical objects Should bind digital annotations with physical objects Real-virtual tours Start with real, guided tour Ubiquitous browse through context information Locate other exhibitions in the vicinity Share your knowledge and experience with others, leave bread-crumbs for others Get the most of the exhibition during your visit

Museums have physical objects

Should bind digital annotations with physical objects

Real-virtual tours

Start with real, guided tour

Ubiquitous browse through context information

Locate other exhibitions in the vicinity

Share your knowledge and experience with others, leave bread-crumbs for others

Get the most of the exhibition during your visit

Conclusions New generation of Internet services can bring digital libraries: Closer to each other (interoperability) Closer to the users (online communities) Social and semantic services delivered in digital libraries can enhance user experience in: E-Learning Real world (!) museums ... and other online and real services JeromeDL is one of the first digital library that aims to implement these services Growing number of JeromeDL instances world-wide: http://wiki.jeromedl.org/Instances

New generation of Internet services can bring digital libraries:

Closer to each other (interoperability)

Closer to the users (online communities)

Social and semantic services delivered in digital libraries can enhance user experience in:

E-Learning

Real world (!) museums

... and other online and real services

JeromeDL is one of the first digital library that aims to implement these services

Growing number of JeromeDL instances world-wide: http://wiki.jeromedl.org/Instances

J eromeDL answer s various expectations as the Digital Library on Social Semantic Information Spaces http://www.jeromedl.org/ http://wiki.jeromedl.org/ Sebastian Ryszard Kruk DERI, NUI Galway, Ireland [email_address]

J eromeDL answer s various expectations

as the Digital Library on Social Semantic Information Spaces

http://www.jeromedl.org/

http://wiki.jeromedl.org/

Sebastian Ryszard Kruk

DERI, NUI Galway, Ireland

[email_address]