The underlying data model follows a Composite pattern:

• There are Entry and Group objects.
• A Group isa Entry.
• Groups can hold a number of children Entrys.
• An Entry has a (single) parent Group.

An Entry can represent a number of things. It may be a file on disk, an HTTP URL, an OpenDAP URL, a weblog entry, a field project report, etc.

The only distinction between a Group and an Entry is that Groups are parents of Entrys. All other aspects of the data model are the same.

Below is the definition of the main entries database table. This represents the lowest common denominator of metadata, e.g., name, group structure, type, time range, geobounds.

id	varchar(200)	The entry id. A unique identifier. See below for a discussion of Group ids.
type	varchar(200)	The entry type (e.g., group, file, model, etc). This corresponds to the TypeHandlers
name	varchar(200)	Short name
description	varchar(2000)	Description
parent_group_id	varchar(200)	Parent group
top_group_id	varchar(200)	The group id of the second to last topmost group
user_id	varchar(200)	the creator
resource	varchar(200)	The resource path (e.g., file, url, etc)
resource_type	varchar(200)	The type of the resource
datatype	varchar(200)	allows for subtyping
createdate	timestamp	when it was created
fromdate	timestamp	From date range of the data
todate	timestamp	To date range of the data
south	float8	Geo bounds
north	float8	Geo bounds
east	float8	Geo bounds
west	float8	Geo bounds

Metadata

Each Entry can have any number of further Metadata elements. The Metadata table is shown below. Each Metadata element is managed by a MetadataHandler java class. This class is responsible for showing the create/edit/search forms and for adding the metadata element into other content views (e.g., THREDDDS catalogs). The MetadataHandler uses the attr(1-4) fields in the table to hold the content.

For example, the ThreddsMetadataHandler handles a variety of metadata that shows up in THREDDS catalogs, e.g., creator, link, publisher, project. For each of these types there is a metadata type in the table: thredds.creator, thredds.link, etc. The attr(1-4) is used to hold the content. For example, thredds.link type uses attr1 for the title and attr2 for the url. The thredds.keyword just uses attr1 to hold the keyword. The thredds.publisher uses all 4 attributes.

id	varchar(200)	The id of the metadata element
entry_id	varchar(200)	The entry id. Corresponds to the id in the entries table above.
type	varchar(200)	The metadata type. This defines the MetadataHandler for this element.
attr1	varchar(10000)	content 1
attr2	varchar(10000)	content 2
attr3	varchar(10000)	content 3
attr4	varchar(10000))	content 4