Posted on behalf of Rob Walker...


The purpose of this note is to give the background on standards, both
existing and under development, that are relevant to the Heritage community,
and to suggest how the sector might proceed with this.

Standards
A standard is formally defined as a "document, established by consensus and
approved by a recognised body, that provides, for common and repeated use,
rules, guidelines or characteristics for activities or their results, aimed
at the achievement of the optimum degree of order in a given context".

Standards bodies
The widely recognised standards approving bodies are:
1. BSI - the British Standards Institution. They have a committee IST/36
(Geographic information), responsible for UK standards activities in this
area, and for input to the associated International Standards activities.
This committee comprises members from users and suppliers in both the public
and private sectors and is sponsored by the Association for Geographic
Information (AGI). Relevant standards include BS 7567 National Transfer
Format and BS 7666 Spatial datasets for geographical referencing. For
further details of the work of IST/36, see www.gistandards.org.uk

2. CEN - the European Standards Committee. This had a committee TC 287 for
Geographic information, that produced a number of European pre-standards
(for Quality, Spatial referencing (2), Metadata and Data transfer), but has
now been superseded by ISO activities.

3. ISO - the International Standards Organisation. This has a committee TC
211 for geographic information, with membership from 33 countries and active
participation from the UK. TC 211 is currently producing a series of
standards, many of which are at the Draft International Standard stage
(DIS). For further details of the work of ISO/TC 211 see
www.statkart.no/isotc211

In addition, the OGC, the Open GIS Consortium, a collection of GIS suppliers
is producing standard technical specifications for system interoperability.
They are providing implementation details to ISO 211 standards with the
objective of commercial off-the-shelve software that is conformant to ISO
211 standards. OGC liaise closely with ISO/TC 211. For further details of
the work of OGC see www.opengis.org

Types of standards
GI standards fall into three general categories:
1. Generic standards, which define basic functions (e.g. SQL, XML) - these
are usually produced by ISO;
2. GI industry standards (e.g. the National Grid) - these are usually
produced by industry-sector bodies such as OGC;
3. Standards that are specific to a particular user application area (e.g.
the British Standard BS 7666-1 Specification for street gazetteers) -  these
are usually produced by BSI or bodies representing user sectors.

Production of Standards
The route for producing standards is essentially the same in all cases. A
Working Party, based as broadly as possible from among the user community,
is convened to produce a draft standard. This is vetted by the approval body
to ensure that it is fit for purpose and conforms to basic rules for
standards, before being published for wider public comment. All comments are
considered by an appropriate group of experts, and formally resolved.
Usually, changes are then made to the standard. If these are extensive, a
further public comment phase ensues. The purpose of this is to establish a
consensus. When this has been achieved, the standard goes for formal
approval to the authorising body, and is subject to detailed editorial
refinement.  A periodic review and maintenance process is set up to ensure
that the standard is kept up to date.

Standards for Heritage
Reading the contributions to the first phase of the discussions, it appears
that the requirements for standards for Heritage fall into a number of
general areas:

Data:
This would take the form of a "data model" for heritage "objects", i.e. a
catalogue of entities with their definitions, unique identifiers and key
relationships. There are several standards giving rules for how to do this,
for example DIS 19109 Rules for application schemas and DIS 19110 Feature
cataloguing methodology.

Presentation:
Several respondents have mentioned the need for a standard set of symbols
and representations.  Categorisation of features should be recorded by coded
attribute values stored in the database, rather than by presentation
characteristics as on a map (although some of the more archaic digital
mapping systems do not have a proper database and "hardwire" all the
presentation characteristics with the object). Symbology is purely a
function of display of this data and can be varied with the application (for
example different symbols can be used at different scales of output). DIS
19117 Portrayal defines a methodology for defining and recording symbols.

Spatial referencing:
Spatial references fall two main categories, those based on coordinates and
those based on relationships with associated geographic objects (named
areas, addresses etc), which can have coordinates associated with them. The
main coordinate reference systems are the National Grid (the Irish Grid in
Ireland) and latitude/longitude. An important aspect of coordinates are
their resolution. Although they can be very precise, in many datasets they
are quite coarse and for example may only have a resolution of 1 km or
lower. Coordinates are described in more detail elsewhere by the Ordnance
Survey.

There are many different types of "spatial units". Some are contiguous and
subdivide all space (e.g. local authority areas), while others cover only
specific sites (e.g. SSSIs). It is useful to decide on the different types
of units that should be used (e.g. parishes, districts, counties etc) and
record the characteristics of these, and to create gazetteers of instances
of  units. Relevant standards for this are DIS 19112 Spatial referencing by
geographic identifiers which defines a general gazetteer structure, and BS
7666 Spatial datasets for geographical referencing, which defines gazetteers
for streets and land and property, and a general structure for addresses.

Data quality:
Whilst it is not possible to specify quality levels for all aspects for all
applications, it is important to know the quality of the data in order to
ascertain its fitness for purpose. Standards such as DIS 19113 Quality
principles and DIS 19114 Quality evaluation procedures specify how quality
of data may be described, measured and recorded. The AGI publication
'Guidelines for data quality' provides useful advice.

Data transfer:
Because of the different formats used for recording data, (often complex)
procedures have been developed for transfer of data between systems. This
has led to some sectors adopting a proprietary format (e.g. DXF, various
ESRI formats) for transfers. NTF (BS 7567) was developed for general
transfer of geographic data, and has been used up to now for Ordnance Survey
data. The adoption of GML and the implementation of open systems will
(eventually) resolve this problem. GML can be used for some types of data
(e.g. Ordnance Survey MasterMap), but is still being developed. It will be
proposed as an ISO standard.

Metadata:
Metadata (data about data) is required at two levels. Firstly there is the
data that describes a dataset (traditionally held in the "header" to the
dataset). This includes such things as the description, source, quality,
referencing scheme, maintenance history, etc. Secondly, there is core
metadata for discovery purposes. This is less detailed, but will include
where the dataset can be obtained, and is stored separately in systems such
as the NGDF Metadata service (www.askgiraffe.org.uk).  Standards for
metadata include the Dublin Core (generic) and DIS 19115 Metadata (very
detailed).

Software applications:
There are likely to be a number of standard applications concerned with
analysis of heritage data. Sector-specific standards could be developed as
specifications for GIS suppliers to implement.

Creation of standards for heritage information
The heritage sector will require standards that apply specifically to that
sector. In some cases, what is required may be a heritage implementation of
an existing standard. This is called in standards parlance a "profile" of
the standard. In a nutshell, the actions required to create the standards
are as follows:
1. decide on the standards required - this conference has identified many
requirements;
2. convene working party (parties?) to produce a draft standards - it may
help to include people from other sectors with experience of similar
activities;
3. circulate the draft(s) widely for comment;
4. review and resolve the comments and finalise the standard;
5. publish the standard;
6. determine the revision process.

If a standard is of interest to a wider audience outside the heritage
sector, it may be worth considering submitting it for consideration as a
British Standard.

Conclusion
Adoption of standards brings many benefits of savings in time and cost
resulting from:
- interoperability of data and systems;
- greater understanding of data;
- shorter learning curves and development times.

The Heritage sector should be looking to produce:
- formal standards for heritage data;
- operational codes of practice;
- supporting common datasets.

Cognisance should be taken of activities in other geographic information
sectors, with a view to adopting developments there and adapting them to the
Heritage sector.


Rob Walker
11.10.01

Rob Walker Consultancy
64 Histon Road
Cottenham
Cambridgeshire
CB4 8UD