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XMM-Newton Science Analysis System


dal (dal-1.182.1) [xmmsas_20070708_1801-7.1.0]

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Data Model

The DAL is principally concerned with data organisation and access.

The DAL Data Model organises data into a collection of data sets.

A data set, which, for aesthetic reasons, will be written as the collocation dataset throughout this document, is an attributable set together with an ordered collection of zero or more blocks. Sometimes a dataset is said to be an attributable set or simply attributable.

A block is one of:

• an array
• a table.

An array is an attributable set together with an n-dimensional array (1 « n « 3) of numeric scalars. The scalars all have the same type. Sometimes an array is said to be an attributable set or simply attributable.

A table is an attributable set together with an ordered collection of zero or more columns. Sometimes a table is said to be an attributable set or simply attributable.

A column is an attributable set together with a vector of cells. Sometimes a column is said to be an attributable set or simply attributable. A cell is one of:

• a string
• a scalar
• an n-dimensional array ( 1 « n « 4 ) of scalars

A scalar is one of:

• a numeric scalar
• a boolean

A numeric scalar is one of:

• an integer value with 8 bits of precission
• an unsigned integer value with 16 bits of precission
• an integer value with 16 bits of precission
• an unsigned integer value with 32 bits of precission
• an integer value with 32 bits of precission
• a real value with 32 bits of precission
• a real value with 64 bits of precission

The scalars within a particular array or column all have the same type.

An attributable set, which for the purposes of brevity will be shortened to attributable throughout this document, is the quintuple
{ name, label, setofattributes, setofhistoryrecords, setofcommentrecords }
where:

• name A string which is used to provide unique identification.
• label A textual description.
• setofattributes is a ordered collection of zero or more attributes
• setofhistoryrecords is an ordered collection of zero or more history records. A history record is a string.
• setofcommentrecords is an ordered collection of zero or more comment records. A comment record is a string.

An attribute is a quadruple { name, label, unit, value }, where:

• name A string which is used to provide unique identification.
• label A textual description.
• unit A string which is used to provide information on the units of the data.
• value Supported types are:
  • string
  • integer
  • real
  • boolean