152 lines
4.1 KiB
Plaintext
152 lines
4.1 KiB
Plaintext
Proposal for a more general file format used by H5Part/H5Block
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Authors: Achim Gsell
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Status: Draft
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1. Introduction
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H5X is the file format used by H5Part and H5Block. H5X is designed on
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top of HDF5: A H5X file is a very special HDF5 file.
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+--------------------+
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| Application |
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+--------------------+
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| H5Part/H5Block API |
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+--------------------+
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| H5X API |
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+--------------------+
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| HDF5 API |
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+--------------------+
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| Filesystem of OS |
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+--------------------+
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2. H5X file format specification
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2.1 The root group
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2.1.1 File attributes
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Attributes of the HDF5 root group are called "file attributes". There
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are no restrictions on file attribute names. Supported values are
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scalars and arrays of 64bit integer and 64bit floating point number as
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well as string values, but not arrays of strings.
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2.1.1.1 Predefined file attributes
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__stepname__ (optional)
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See below.
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__stepnumwidth__ (optional)
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See below.
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2.1.2 Members of the root group
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Members of the root group are special formated HDF5 groups called
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"step groups". The name of a step group is "<name>#<number>".
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Whereby <name> is either defined by the optional file attribute
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__stepname__ or set to "Step" by default. <number> is an
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unsigned integer less than 2^63.
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/
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+- Step#0
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+- Step#1
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...
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+- Step#n
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+- StepProperties [NEW]
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+- Mesh [NEW]
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The optional file attribute __stepnumwidth__ defines the minimum width
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of <number> in the name of the step group. The number is padded with
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'0'. The minimum width defaults to zero, so that no paddings occurs.
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Example: With __stepnumwidth__ := 5 the name of the step group with
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number 42 is "Step#00042", with __stepnumwidth__ := 0 the name is
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"Step#42".
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Step groups may be unsorted in the HDF5 file und may not be number
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consecutively.
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2.2 Format of a step group
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2.2.1 Step attributes
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Step attributes are HDF5 attributes asigned to a step group. There
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are no restrictions on file attribute names. Supported values are
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scalars and arrays of 64bit integer and 64bit floating point number as
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well as string values, but not arrays of strings.
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2.2.2 Predefined step attributes
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No predefined step attributes exists.
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2.2.3 Members of a step group
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Members of a step group are HDF5 datasets and optional one HDF5 group
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with the name "Block". HDF5 datasets in a step group are called "step
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datasets". The optional block group is called "block data".
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Mesh?!
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2.2.4 Step datasets
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Step datasets are arrays of rank 1. The dataset size must be the same
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for all datasets inside a step. The size of the dataset may vary
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from step to step. Array values are 64bit integer or 64bit floating
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point numbers. No limitations (other than given by HDF5) are given on
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step dataset names.
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2.2.5 Block Data
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The block data group is a container for an arbitrary number of field
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data. A field is a data structure to store arrays of rank m with
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n-dimensional vector values. Fields are represented within HDF5
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groups. The HDF5 group name is the unique identifier for a field in
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the current step.
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2.2.5.1 m-rank fields with n-dimensional-vector values
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Values are stored per dimension in separate datasets. Thus we have n
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datasets for a field with n-dimensional vector values. Each dataset
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corresponse to one dimension. The datasets are numbered from '0' to
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'n-1'. Arrays are stored in column major order (Fortran indexing
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scheme).
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/ # HDF5 root group
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...
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+- Step#<i> # HDF5 group
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+- Block # HDF5 group
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+- <field name> # HDF5 group
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+- 0 # HDF5 dataset, first dim of vector
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+- 1 # HDF5 dataset, second dim of vector
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...
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+- n-1 # HDF5 dataset, last dim of vector
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...
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2.2.5.2 m-rank fields with scalar values
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Fields with scalar values are stored as special case of fields with
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n-dimensional vector values with n := 1.
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/ # HDF5 root group
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...
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+- Step#<i> # HDF5 group
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+- Block # HDF5 group
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+- <field name> # HDF5 group
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+- 0 # HDF5 dataset, scalar value
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...
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2.3 Step properties [NEW]
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