As mentioned in Documenting and archiving, the Archive consists of three main components: (i) geophysics data, (ii) project material and (iii) project documentation. The latter includes geophysics metadata, geophysics georeferencing, project metadata and file description. The metadata can be thought of as that information that can easily be stored in a database and Comprehensive documentation introduces a comprehensive list of metadata fields that are most relevant for the documentation of archaeological geophysical projects. However, some Archiving Bodies store only a subset of these fields in their database or may use slightly different field names, thereby often only offering a subset of the Comprehensive Documentation. In addition, they may insist on the use of particular term lists. When compiling the relevant metadata, for example in an in-house database, it is advisable to start with a fairly comprehensive set of documentation and then ‘thin it out’ according to what the selected Archiving Body can hold. If the characteristics of these varying practices were captured in XML schemas and RDF vocabularies, automatic translators could be designed to facilitate simple data exchange.

To illustrate subsets of the Comprehensive Documentation it is useful to look at the ADS archive and the ADS ArchSearch database, the OASIS database, and the English Heritage geophysical survey database (EH GSdb). Out of these only the ADS can be considered an Archiving Body as it provides full archiving services for data and metadata, with data migration, preservation and accessibility (Level 4 – Accessible Archiving, in The archive and the archiving body). However, its main search interface, ArchSearch, uses only a subset of the metadata (derived from Dublin Core metadata) when facilitating the discovery of the Archive over the Internet. In contrast, OASIS and the EH GSdb use a very full subset of the Comprehensive Documentation but do not store the rest of the Archive, like data files, georeferencing information etc. Table 5 provides the mapping of metadata fields between the Comprehensive Documentation of Subsets of documentation and OASIS, the EH GSdb and the fields used in ArchSearch. Other Archiving Bodies and database holders will also have developed relevant data structures for their databases and mapping these subsets to the Comprehensive Documentation should not pose too much of a problem.

Table 5: Mapping of documentation: Comprehensive, OASIS, EH GSdb, ArchSearch.

Project Information
Comprehensive Documentation	OASIS Form Field	EHGSdb	Dublin Core (ArchSearch)
Survey name	Project Details: Project Name	Project Title	Project Title
Survey index	Project Details: Identifier; Type	Survey index	Identifiers
Survey purpose	Project Details: Type of Project; Description	Purpose of Survey	Description
Report summary	Project Details: Description	Synopsis of report content	Description
Bibliographic references	Project Bibliography section	Bibliographic References	Relations
Survey keywords	Project Details: Monument Type; Significant Finds	Archaeological Feature Classifications	Subject
Spatial coverage	Project Location: Study Area; Site Coordinates	Grid Reference	Coverage
Administrative area	Project Location: District/Unitary Authority; Parish	County/Unitary Authority	Coverage
State	Project Location: County		Coverage
Country	(England; Scotland; Wales depending on form used.)	Country	Coverage
Solid geology	Project Details – Geophysics: Solid Geology	Solid Geology
Drift geology	Project Details – Geophysics: Drift Geology	Drift Geology
Duration	Project Details: Project Dates	Occurred between	Dates
Weather		Weather
Soil condition
Land use	Project Details: Current Land Use	Land use
Monument type	Project Details: Monument Type	Monuments covered	Subject
Monument period	Project Details: Period	Monument period	Coverage
Scheduled Ancient Monument (SAM) number	Project Details: Identifier (Type = ‘SM No.’)	Scheduled Ancient Monument (SAM) number	Identifiers
Surveyor	Project Creators: Name of Organisation; Project Director/Manager; Project Supervisor	Surveyor/Personnel	Creators
Client	Project Creators: Project Brief Originator; Type of Sponsor/Funding Body	Client	Creators
Depositor	Project Creators: Name of Organisation	Depositor	Creators
Primary archive	Project Archives: Physical; Digital; Paper – all fields	Primary archive	Relations
Related archives	Project Archives: Physical; Digital; Paper – all fields	Related archives	Relations
Copyright		Copyright	Copyright
Term list	Dependent on Monument / Artefact fields and location of site (i.e. relevant English, Scottish, Welsh lists)
Geophysics Metadata
Comprehensive Documentation	OASIS Form Field	EHGSdb	Dublin Core (ArchSearch)
Survey type	Techniques	Geophysical Techniques Used	Resource Type
Instrumentation	Project Details – Geophysical techniques: Instrumentation / Instrument Type	Instrument Type/Instrument make
Reasons for choice of survey technique
Area surveyed	Project Details – Geophysical techniques: Size of Survey Area	Area Surveyed
Method of coverage		Method of coverage
Traverse separation	Project Details – Geophysical techniques: Traverse Separation	Traverse Separation
Line separation
Reading interval	Project Details – Geophysical techniques: Reading Interval	Reading Interval
Sampling position
Data grid size
Accuracies
Additional remarks	Project Details – Geophysical techniques: Notes	Comments on Survey
Earth Resistance Surveys
Comprehensive Documentation	OASIS Form Field	EHGSdb	Dublin Core (ArchSearch)
Electrode configuration	Project Details – Geophysical techniques: Resistivity: Electrode Configuration	Electrode configuration
Electrode spacing	Project Details – Geophysical techniques: Resistivity: Electrode Separation; Electrode Separation Qualifier	Electrode separation
Multiple configurations
Magnetometer Surveys
Magnetic north
Instrument drift
Low Frequency Electromagnetic Surveys
Coil configuration	Project Details – Geophysical techniques: Electromagnetic: Coil Separation; Frequency; Phase
Recorded component	Notes
Ground Penetrating Radar Surveys
Comprehensive Documentation	OASIS Form Field	EHGSdb	Dublin Core (ArchSearch)
Antenna information	Project Details – Geophysical techniques: Ground Penetrating Radar: Centre Frequency of Antennae
Timing information	Project Details – Geophysical techniques: Ground Penetrating Radar: Time Window;
Average subsurface velocity	Project Details – Geophysical techniques: Ground Penetrating Radar: Average Subsurface Velocity
Maritime Sonar Surveys
Comprehensive Documentation	OASIS Form Field	EHGSdb	Dublin Core (ArchSearch)
Average water velocity	Project Details – Geophysical techniques: Marine – multibeam echosounder: Average Water Velocity
Sonar frequency	Project Details – Geophysical techniques: Marine – multibeam echosounder: Frequency
Beam width at nadir	Project Details – Geophysical techniques: Marine – multibeam echosounder: Beam Width Nadir
Survey Methodology
Comprehensive Documentation	OASIS Form Field	EHGSdb	Dublin Core (ArchSearch)
Data grid layout
Data grid size
Resolution
Survey direction
Line sequence
Drift value
Bias value
Report
Comprehensive Documentation	OASIS (form field titles – not DB fields)	EHGSdb	Dublin Core (ArchSearch)
Report title	Project Bibliography: Title	Report Title
Report reference number	Project Bibliography: Other bibliographic details	Report Number
Report author	Project Bibliography: Author / Editor	Author/Report Date
Report holder	Project Bibliography: Place of Issue or Publication	Report held by

In addition, the term list used for the field Survey type differs between different organisations, as indicated in Table 6. The mapping between them is straight forward.

Table 6: Term lists for the field Survey type

Comprehensive Documentation	OASIS	EH GSdb
Magnetometer Survey (land based)	Magnetometry	Magnetometer
Magnetometer Survey (marine)	Marine – Magnetometry
Magnetic Susceptibility (volume- or mass specific susceptibility); including random samples, gridded, lab based measurement of samples and field based in-situ measurements”	Magnetic Susceptibility	Magnetic Susceptibility
Earth Resistance Survey	Resistivity – Area	Resistivity
Electrical Resistivity Imaging (ERI); including pseudosections and tomography	Resistivity – Profile	Resistivity Profile
Vertical Electrical Sounding (VES)		Resistivity Depth Sounding
Electrostatic Survey
Low Frequency Electromagnetic	Electromagnetic	Electro-magnetic Survey
Ground Penetrating Radar (GPR)	Ground Penetrating Radar	Ground Penetrating Radar
Seismic	Seismic	Seismic Refraction
Microgravity	Microgravity	Microgravity
Magnetotelluric
Very Low Frequency Electromagnetic (VLF)
Radioactivity
Side Scan Sonar (SSS)	Marine – Side Scan Sonar
Singlebeam Echosounder	Marine – Singlebeam Echosounder
Multibeam Echosounder	Marine – Multibeam Echosounder
Sub-bottom Profiler	Marine – Sub-bottom Profiler