IHO 2002

2002 National Report for IHO

 

 

IHO HYDROGRAPHIC METADATA REQUIREMENTS

 

Michael Huet

International Hydrographic Bureau

Monaco, France

Background

Metadata elements which are embedded in the current edition of the IHO Transfer Standard for Hydrographic Data (known as S-57) do not conform to international metadata standards and are considered inadequate for future data discovery, retrieval and reuse. As a result, it has been agreed that metadata should be considered as a Work Item for the further development of S-57 by the relevant IHO body in charge of maintaining this Standard (TSMAD – Transfer Standard Maintenance and Application Development Working Group). The following information paper, prepared by Mr Anthony Pharaoh (IHB) in support of the study, outlines the need to develop an IHO metadata profile for hydrographic data. An action plan is also provided.

 

Introduction

In the paper chart world, metadata is displayed in the title block of charts, and may also be recorded in various chart catalogues. In this form, metadata is readily apparent and easily transferred between chart producers and users. When charts are in a digital form, metadata is equally as important, but its development and maintenance often require a more conscious effort on the part of data producers and subsequent users. Increasingly, hydrograhpic organizations are collecting, storing and archiving large quantities of digital data. The complexity and diversity of these data have increased over the past decade. They are no longer confined to digital source and reproduction files, (used for paper chart generation), but now also include a variety of digital nautical products. Digital hydrographic data holdings are becoming an important national asset that must be managed and controlled. In order to achieve this, Hydrographic Organizations will need to record information about the data (i.e. metadata) and make it available for easy accesses. As hydrographic data holdings proliferate, a common metadata standard, will facilitates the management, dissemination and reuse of digital data.

 

Benefits of a Metadata

Metadata allows a producer to describe a dataset fully so that users can understand the assumptions and limitations of the data, and can evaluate the dataset’s applicability for its intended use. As personnel change within an organization, data may lose their value if the meta information is not properly recorded. The documentation of metadata may seem burdensome, however a lack of knowledge about an organizations data can lead to duplication of effort, inefficiency and the loss of revenue. Metadata is also important element in the creation of a spatial data clearinghouse, where potential users can search for the data they need for their intended application. (A Geospatial Data Clearinghouse is a location, typically accessed through the World Wide Web (WWW), which provides information about the availability of the spatial data holdings of an organization).

 

Examples of Metadata

 

Data Identification: Title, Area covered, Themes, Currentness, Restrictions.

Data Quality: Accuracy, Completeness, Logical Consistency, Lineage.

Spatial Data Organization: Vector, Raster, Type of elements, Number.

Spatial Reference: Projection, Grid system, Datum, Coordinate system.

Entity and Attribute Information: Features, Attributes, Attribute values.

Data Distribution: Distributor, Formats, Media, Price.

Metadata Reference: Metadata currentness, Responsible party.

Within S-57, meta data has been defines at three levels, namely, at the dataset level, the object level, and at the attribute level. The scope of metadata elements presently defined in S-57 (especially at the dataset level) do not conform with international metadata standards and are no longer adequate for future data discovery, retrieval and reuse of the increasingly diverse data holding of most hydrographic organizations.

 

Types of Metadata Queries may include:

Queries about data entities:

– What is the data?

– Where is the data?

– What are the data characteristics?

– Where did this data come from?

– What is the quality (accuracy, lineage, resolution) of this data?

The basic metadata queries about process entities:

– What can one do with this data?

– What types of spatial and geometric operators are available?

– How can data be imported (acquired)?

– How can entities like various data layers and spatial objects, be created, deleted and updated?

– How can the results of analysis be presented?

 

Conceptual Models for Metadata Management

There is a close relationship between data and metadata. The form of this relationship depends on the models for both data and metadata. The conceptual model for hydrographic data will have to describe the actual data and the natural relationships found in that data. A good conceptual model should be meaningful to both database managers and the non-technical end users. Metadata should also include information that allows data identification and selection based on the properties of data such as content, sources and quality. It must therefore be efficiently and effectively accessible for a range of procedures.

 

Note: This usually calls for a database management system, since metadata is also data. In some data models, part of metadata is an integral part of the data itself which is referred to as a self-describing database (Typically found in the Object Oriented Database Management Systems). However in most relational databases, metadata, is stored in separate deductive (meta)data layers. Most DBMSs contain a data dictionary, which is used by the DBMS itself for data definition and for maintaining data integrity. Data dictionaries may be accessible for metadata queries by users.

 

The need for standardization

The full potential of metadata, should not only be considered at the isolated database level, but also as a distribution of separate databases that may be spread over a wide geographical area. This model requires the use of a common data standard and metadata standard. Although it has been decided that future extensions to S-57 will be based on the ISO/TC211 suite of standards, for the purposes of this study, it is recommended that the US FGDC Content Standard for Digital Geospatial Metadata should also be considered.

 

US Federal Geographic Data Committee (FGDC) – Content Standard for Digital Geospatial Metadata

This standard specifies the information content of metadata for a set of digital geospatial data. It was designed to help prospective users of geospatial data to determine what data exists, the fitness of this data for their applications, and the conditions for accessing the data. The standard establishes the names (and groups) of metadata elements, their definitions, and information about the values that are to be provided for the metadata elements. It specifies the elements needed to support three major uses of metadata: (1) to maintain an organization’s internal investment in geospatial data, (2) to provide information to data clearinghouses and catalogs, and (3) to provide information needed to process and interpret data transferred from another organization. The standard establishes a common set of terminology and definitions for concepts related to metadata, including:

– the names of data elements and compound elements (groups of data elements) to be used,

– the definitions of these compound and data elements, and

– information about the values that are to be provided for the data elements.

The standard specifies information content, but not how to organize this information in a computer system or in a data transfer, or how to transmit, communicate, or present the information to a user. The standard supports the development of profiles that enable the based definition of a subset of the metadata entities and/or elements that are used by a specific discipline or organization. (A profile is subset of the metadata entities and elements of the base standard that describes the application of the CSDGM Standard to a specific user community. Profiles may also contain extended elements. See – “Shoreline Metadata Profile of the Content Standards for Digital Geospatial Metadata”)

ISO TC211 DIS 19115 – Geographic information – Metadata

This International Standard defines metadata elements, provides a schema and establishes a common set of metadata terminology, definitions, and extension procedures. When implemented this International Standard will:

  • Provide data producers with appropriate information to characterize their geographic data properly.
  • Facilitate the organization and management of metadata for geographic data.
  • Enable users to apply geographic data in the most efficient way by knowing its basic characteristics.
  • Facilitate data discovery, retrieval and reuse. Users will be better able to locate, access, evaluate, purchase and utilize geographic data.
  • Enable users to determine whether geographic data in a holding will be of use to them.
  • An important component of the standard is the data dictionary which describes the characteristics of the metadata.

The standard also makes provision for metadata extensions and profiles. The following types of extensions are allowed:

  • adding a new metadata section;
  • creating a new metadata codelist to replace the domain of an existing metadata element that has “free text” listed as its domain value;
  • creating new metadata codelist elements (expanding a codelist);
  • adding a new metadata element;
  • adding a new metadata entity;
  • imposing a more stringent obligation on an existing metadata element;
  • imposing a more restrictive domain on an existing metadata element.

 

The creation of an IHO community profile based on the ISO/TC211 metadata standard 19115.

This International Standard 19115 defines almost 300 metadata elements, with most of these being listed as “optional”. They are explicitly defined in order to help users understand exactly what is being described. If extensive additional metadata elements are required for IHO use, it may be necessary to develop a “community profile”. This may require that a specific set of metadata elements are defined as mandatory (i.e. certain existing optional metadata elements may need to be defined as mandatory for IHO use). For IHO requirements we may want to establish additional metadata elements that are not in this International Standard. For example, it may be necessary to develop metadata elements for the status of datasets within a system to help manage production. However, these added elements will not be known outside the community unless they are published.

 

Note: A community profile should also describe issues such as field sizes and domains for all metadata elements. If one system within a community uses thirty-two characters for the title of a dataset and another system handles eight characters, interoperability will not be achieved. Standardizing selected domains within a community is important to allow more efficient searches and better system control. Community profiles are described in ISO 19106.

 

Conclusion

The information needed to create metadata is often readily available when the data are collected or produced. A small amount of time invested at the beginning of a project may save money in the future. Data producers and users cannot afford to be without documented data. The initial expense of documenting data clearly outweighs the potential costs of duplicated or redundant data generation. However in the absence of an IHO metadata standard, harmonization of metadata information between member organization can not be achieved. Metadata has also been recognised as a key element for the development of national and global spatial data infrastructures.

 

Action Plan

 

The following actions, aiming at developing a Hydrographic Metadata Dictionary, are to be completed by TSMAD by October 2002:

  • List all hydrographic metadata element/entities;
  • Match hydrographic metadata elements/entities to 19115;
  • Review obligation/condition requirements (mandatory vs optional);
  • Review occurrence and data type fields;
  • Identification/documentation of additional hydrographic metadata elements.

© Copyright, ICA Standards Commission, 2002