Database Reference
In-Depth Information
Logical file metadata
: Metadata attributes associated with the logical file in-
clude the following. A
logical file name
attribute specifies a name that
is unique within the namespace managed by a metadata service. A
data
type
attribute describes the data item type, for example, whether the
file format is binary, html, XML, and so forth. A
valid
attribute indi-
cates whether a data item is currently valid, allowing users to quickly
invalidate logical files, for example, if the file administrator determines
that a logical file contains incorrect data. If data files are updated over
time, a
version
attribute allows us to distinguish among versions of a
logical file. A
collection identifier
attribute allows us to associate a log-
ical file with exactly one logical collection.
Creator
and
last modifier
attributes record the identifications of the logical file's creator and last
modifier. Other attributes specify the
creation time
and the
last modifi-
cation time
.A
master copy
attribute can contain the physical location
of the definitive or master copy of the file for use by higher-level data
consistency services.
Logical collection metadata:
Attributes include the
collection name
and a
description of the
collection contents
, which consist of the list of logical
files and other logical collections that compose this collection. Each log-
ical file can belong to at most one logical collection. Logical collections
may contain other collections, but must form an acyclic collection hier-
archy. In addition, the collection metadata includes a
text description
of
the collection, information about the
creator
and
modifiers
of the col-
lection, and
audit
information. Finally, there may be a
parent
attribute
that records the identifier of the parent logical collection. There may be
an arbitrarily deep acyclic hierarchy of logical collections.
Logical view metadata:
Attributes include the
logical view name
and
descrip-
tion
; information about the logical files, logical collections, and other
logical views that compose this logical view; attributes describing the
creator
and
modifiers
of the view; and
audit
information.
Authorization metadata:
Attributes are used to determine the
access permis-
sions
to the data items and metadata.
User metadata:
Attributes that describe
writers of metadata
, including con-
tact information. The attributes specify the distinguished
name, de-
scription, institution, address, phone,
and
email
information for writers.
User-defined metadata
attributes: Extensibility of the schema beyond pre-
defined attributes is provided by allowing users to define new attributes
and associate them with logical files, collections, or views. Extensibility
is an essential requirement in metadata systems, since each scientific
application domain typically produces one or more metadata schemas
that capture attributes of interest to that community.
Annotation
attributes: Annotations can be attached to logical files, collec-
tions, or views. Annotation metadata includes the
identifier
for the
