/* * QDataSet.java * * Created on January 25, 2007, 9:12 PM * * To change this template, choose Tools | Template Manager * and open the template in the editor. */ package org.das2.qds; /** *

QDataSets are less abstract and more flexible data model for das2. das2's * old data model was developed to deliver spectrogram time series data sets * where the dataset structure would change over time, and the interface is highly * optimized for that environment. It's difficult to express many datasets in these * terms, so the simpler "quick" QDataSet was introduced.

* *

The QDataSet can be thought of as a fast java array that has name-value metadata * attached to it. These arrays of data can have arbitrary rank, although currently * the interface limits rank to 0,1,2,3, and 4. (Rank N is proposed but not * developed.) Each dimension's length can vary, like Java arrays, and datasets * where the dimensions do not vary in length are colloquially called "Qubes."

* *

QDataSets can have other QDataSets as property values, for example the property * QDataSet.DEPEND_0 indicates that the values are dependent parameters of the "tags" * QDataSet found there. This how how we get to the same abstraction level of * the legacy Das2 dataset.

* *

This is inspired by the CDF data model and PaPCo's dataset model.

* * @see http://autoplot.org/QDataSet * @author jbf */ public interface QDataSet { /** * type QDataSet, this dataset is a dependent parameter of the independent parameter represented in this DataSet. * The tags for the DataSet's 0th index are identified by this tags dataset. */ public final static String DEPEND_0="DEPEND_0"; /** * type QDataSet, this dataset is a dependent parameter of the independent parameter represented in this DataSet. * The tags for the DataSet's 1st index are identified by this tags dataset. When DEPEND_1 is rank 2, * then its first dimension goes with DEPEND_0 and its second are the tags for the second dimension. */ public final static String DEPEND_1="DEPEND_1"; /** * type QDataSet, this dataset is a dependent parameter of the independent parameter represented in this DataSet. * The tags for the DataSet's 2nd index are identified by this tags dataset. When DEPEND_2 is rank 2, * then it's first dimension goes with DEPEND_0 and it's second are the tags for the second dimension. */ public final static String DEPEND_2="DEPEND_2"; /** * type QDataSet, this dataset is a dependent parameter of the independent parameter represented in this DataSet. * The tags for the DataSet's 3nd index are identified by this tags dataset. When DEPEND_3 is rank 2, * then it's first dimension goes with DEPEND_0 and it's second are the tags for the second dimension. */ public final static String DEPEND_3="DEPEND_3"; /** * type QDataSet describing each of the bundled datasets (Bundle Descriptor). This dataset describes * how the columns should be split up * into separate parameters. This rank 2 dataset has a length that is equal to the number * of bundled datasets. The values(i,*) are the qube dimensions of the dataset, * except for the first dimension. When all the bundled datasets are rank 1, then * length(*) will be equal to zero. property(*,UNITS) will yield the unit for each * dataset. Bundle dimensions generally add one physical dimension for each * bundled dataset. property(*,DEPEND_0) is special, because it will return a string * rather than a QDataSet. This string should refer to one of the bundled datasets by * its NAME property. (Any property that returns a QDataSet should return a * string referring to another dataset in the bundle.) Also the dataset is necessarily * a QUBE. */ public final static String BUNDLE_1="BUNDLE_1"; /** * type QDataSet describing each position of the rank 1 dataset (Bundle Descriptor). This dataset describes how the columns should be split up * into separate parameters. See BUNDLE_1. Note slicing a dataset on the zeroth * dimension will move BUNDLE_1 to BUNDLE_0. * Properties defined in this dataset will be overwritten by the BUNDLE dataset's properties. * For example, if the dataset has property( UNITS, 0 ) defined as "Hz" but the * bundle has property( UNITS,0 ) as "Hertz" then "Hertz" is used. */ public final static String BUNDLE_0="BUNDLE_0"; /** * type QDataSet Bundle Descriptor. When multiple BUNDLES are present, they must be simple bundles, bundling just * rank 1 datasets. */ public final static String BUNDLE_2="BUNDLE_2"; /** * type QDataSet Bundle Descriptor. When multiple BUNDLES are present, they must be simple bundles, bundling just * rank 1 datasets. */ public final static String BUNDLE_3="BUNDLE_3"; /** * type Integer, only found in a bundle descriptor (BUNDLE_0 or BUNDLE_1), this returns the integer * index of the start of the current dataset. If this is null, then the index used to access * the value may be used. (E.g. a bundle of Rank 1 datasets.) */ public final static String START_INDEX="START_INDEX"; /** * type String which is a comma-delimited list of keywords that describe the boundary * type for each column. For example, "min,max" "min,maxInclusive" or "c95min,mean,c95max". * A bins dimension doesn't add a physical dimension. Autoplot uses just "min,max" and "min,maxInclusive" */ public final static String BINS_1="BINS_1"; /** * type String which is a comma-delimited list of keywords that describe the boundary * type for each column. This comma-delimited list of keywords that describe the boundary * type for each column. For example, "min,max" "min,maxInclusive" or "c95min,mean,c95max". * A bins dimension doesn't add a physical dimension. Autoplot uses just "min,max" and "min,maxInclusive" */ public final static String BINS_0="BINS_0"; /** * type String, non-null string identifies that elements in this dimension are * instances of data with the same dimensions. ds[2,20] where JOIN_0="DEPEND_1" should * be equivalent to ds[40]. It's not clear if the text should indicate anything, but * for now let's just indicate the next dimension. */ public final static String JOIN_0="JOIN_0"; /** * type QDataSet, a correlated plane of data. An additional dependent DataSet that is correlated by the first index. * Note "0" is just a count, and does not refer to the 0th index. All correlated datasets must be * correlated by the first index. TODO: what about two rank 2 datasets? * Note that if PLANE_i==null then PLANE_(i+1) must also be null. */ public final static String PLANE_0= "PLANE_0"; /** * type QDataSet, that stores the position of a slice or range in * a collapsed dimension. In "Flux(Energy) @ Time=2009-03-16T11:19 UT", the Time=... comes from * a context property. Note "0" is just a count, and does not refer to the 0th index. * A dataset can have any number of contexts: * Temperature @ ( Time, Long, Lat ): 37 deg F @ ( 2009-03-16T11:19 UT, 91.5331 deg West, 41.6579 deg North ) * Typically this will be a rank 0 dataset, but may also be a rank 1 dataset with a bins dimension. */ public final static String CONTEXT_0= "CONTEXT_0"; /** * type QDataSet, that stores the position of a slice or range in * a collapsed dimension. In "Flux(Energy) @ Time=2009-03-16T11:19 UT", the Time=... comes from * a context property. Note "1" is just a count, and does not refer to the 1th index. * A dataset can have any number of contexts: * Temperature @ ( Time, Long, Lat ): 37 deg F @ ( 2009-03-16T11:19 UT, 91.5331 deg West, 41.6579 deg North ) * Typically this will be a rank 0 dataset, but may also be a rank 1 dataset with a bins dimension. */ public final static String CONTEXT_1= "CONTEXT_1"; /** * the maximum number of allowed planes. This should be used to enumerate all the planes. */ public final static int MAX_PLANE_COUNT=50; /** * maximum number of same-unit bundled dimensions (e.g. B_GSM[time,Bundle]). This was introduced when cdf dataset * fa_k0_tms_20040224_v01.cdf?O+_en had 48 energy channels, was marked as time_series but wouldn't render because * view code limited to 12. * * Seth's file vap+cdf:file:///home/jbf/ct/hudson/data.backup/cdf/lanl/rbspa_pre_ect-mageisHIGH-sp-L1_20130213_v1.0.0.cdf?Count_Rate_elec * RBSP/Hope has 72 channels. */ public final static int MAX_UNIT_BUNDLE_COUNT=96; /** * the highest rank supported by the library. Arbitrary high rank datasets are supported through * RankNDataSet, but must be sliced to be accessed. */ public static int MAX_RANK=4; /** * the highest rank supported by the library, without direct access * to datums. Some codes may choose to use this when supporting high rank * data is trivial. */ public static int MAX_HIGH_RANK=8; /** * type Units indicating the units of the dataset in the enumeration of * org.das2.datum.Units, as in org.das2.datum.Units.km. New unit types * can be introduced with Units.lookup. For example, * 
     *from org.das2.datum import Units
     *u= Units.lookupUnits('seconds since 2015-001T00:00')
     *ds= findgen(3600)
     *ds= putProperty( ds, QDataSet.UNITS, u )
     *plot( ds )  # plots line from 00:00 to 01:00.
     *
* @see org.das2.datum.Units */ public final static String UNITS="UNITS"; /** * type String, Java/C format string for formatting the values. This * should imply precision, and codes that serialize data can use this * to correctly format the data. Examples include: */ public final static String FORMAT="FORMAT"; /** * type Number, value to be considered fill (invalid) data. Note because * all data is accessed as doubles, noise may be inadvertently affect numbers. */ public final static String FILL_VALUE="FILL_VALUE"; /** * type Number, minimum bounding measurements to be considered valid. Lower * and Upper bounds are inclusive. FILL_VALUE should be used to make the * lower bound or upper bound exclusive. Note DatumRange contains logic is * exclusive on the upper bound. */ public final static String VALID_MIN="VALID_MIN"; /** * type Number, maximum bounding measurements to be considered valid. Lower * and Upper bounds are inclusive. FILL_VALUE should be used to make the * lower bound or upper bound exclusive. Note DatumRange contains logic is * exclusive on the upper bound. */ public final static String VALID_MAX="VALID_MAX"; /** * type Number that is min used to discover datasets. This should be a reasonable representation * of the expected dynamic range of the dataset. */ public final static String TYPICAL_MIN="TYPICAL_MIN"; /** * type Number that is the max used to discover datasets. This should be a reasonable representation * of the expected dynamic range of the dataset. */ public final static String TYPICAL_MAX="TYPICAL_MAX"; /** * String, "linear" or "log", hinting at the preference for linear or a log * axis. */ public final static String SCALE_TYPE="SCALE_TYPE"; /** * String, Concise Human-consumable label suitable for a plot label (~10 chars). */ public final static String LABEL="LABEL"; /** * String, Human-consumable string suitable for a plot title (~100 chars). */ public final static String TITLE="TITLE"; /** * String, Human-consumable string suitable for describing the data more fully. * This should be html text, or just a link to other documentation (one URL, * or two sentences to one page of text). */ public final static String DESCRIPTION="DESCRIPTION"; /** * QDataSet, dataset of same geometry that indicates the weights for each point. Often weights are computed * in processing, and this is where they should be stored for other routines. When the weights plane is * present, routines can safely ignore the FILL_VALUE, VALID_MIN, and VALID_MAX properties, and use non-zero weight to * indicate valid data. Further, averages of averages will compute accurately. */ public final static String WEIGHTS="WEIGHTS"; /** * Boolean, Boolean.TRUE if dataset is monotonically increasing, and the data is rank 1. * Data may only contain invalid values at the beginning or end, and may contain repeated * values. Generally this will be used with tags datasets. */ public final static String MONOTONIC="MONOTONIC"; /** * QDataSet of rank0, which is the expected distance between successive * measurements where it is valid to make inferences about the data. * For example, interpolation is disallowed for points 1.5*CADENCE apart. * This property only makes sense with a tags dataset. Note this may be * a "ratiometric" datum, like 110 percentIncrease, for logarithmically * spaced data. Cadence must be positive. */ public final static String CADENCE="CADENCE"; /** * QDataSet of rank 0, or correlated QDataSet that limits accuracy. This should * be interpreted as the one standard deviation confidence level, and must * be positive. * @see #BIN_PLUS for measurement intervals. */ public final static String DELTA_PLUS="DELTA_PLUS"; /** * QDataSet of rank 0, or correlated QDataSet that limits accuracy. This should * be interpreted as the one standard deviation confidence level, and must * be positive. * @see #BIN_MINUS for measurement intervals. */ public final static String DELTA_MINUS="DELTA_MINUS"; /** * QDataSet of rank 0 or correlated QDataSet identifies boundary. This is added to the * measurements and should be interpreted as the upper limit of 100% confidence * interval where a measurement was collected. * Note if both DELTA_PLUS and BIN_PLUS are found, * then BIN_PLUS must be greater than DELTA_PLUS. * @see #DELTA_PLUS for one-standard deviation confidence interval. */ public final static String BIN_PLUS="BIN_PLUS"; /** * QDataSet of rank 0 or correlated QDataSet identifies boundary. This is subtracted from the * measurements and should be interpreted as the lower limit of the 100% confidence interval where a measurement was collected. * @see #DELTA_MINUS for one-standard deviation confidence interval. */ public final static String BIN_MINUS="BIN_MINUS"; /** * QDataSet of rank 1 identifies boundary in the same units as the dataset. * This should be interpreted as the upper limit of 100% confidence * interval where a measurement was collected. When this is found, BIN_PLUS * and BIN_MINUS should be ignored. * @see #BIN_PLUS which is the offset. */ public final static String BIN_MAX="BIN_MAX"; /** * QDataSet of rank 1 identifies boundary in the same units as the dataset. * This should be interpreted as the lower limit of the 100% confidence * interval where a measurement was collected. When this is found, BIN_PLUS * and BIN_MINUS should be ignored. * @see #BIN_MINUS which is the offset. */ public final static String BIN_MIN="BIN_MIN"; /** * name of the dataset in a bundle to be connected to BIN_MIN. */ public final static String BIN_MIN_NAME="BIN_MIN_NAME"; /** * name of the dataset in a bundle to be connected to BIN_MAX. */ public final static String BIN_MAX_NAME="BIN_MAX_NAME"; /** * name of the dataset in a bundle to be connected to BIN_MINUS. */ public final static String BIN_MINUS_NAME="BIN_MINUS_NAME"; /** * name of the dataset in a bundle to be connected to BIN_PLUS. */ public final static String BIN_PLUS_NAME="BIN_PLUS_NAME"; /** * name of the dataset in a bundle to be connected to DELTA_PLUS. */ public final static String DELTA_PLUS_NAME="DELTA_PLUS_NAME"; /** * name of the dataset in a bundle to be connected to DELTA_MINUS. */ public final static String DELTA_MINUS_NAME="DELTA_MINUS_NAME"; /** * CacheTag, indicating the coverage and resolution of a dimension. This is * an object that represents * the coverage and resolution of the interval covered. For example, in Autoplot * the TimeSeriesBrowse uses this to keep track of what's already been read. */ public final static String CACHE_TAG="CACHE_TAG"; /** * String, hint as to preferred rendering method. Examples include "spectrogram", "time_series", and "stack_plot", * "nnSpectrogram", "hugeScatter", "series", "scatter", "colorScatter", "stairSteps", "fillToZero" * "digital", "image", "pitchAngleDistribution", "eventsBar". Note these are just suggestions and are not * interpreted in the library. */ public final static String RENDER_TYPE="RENDER_TYPE"; /** * full-fidelity rendering of buckshot and connect-a-dot plots */ public final static String VALUE_RENDER_TYPE_SERIES="series"; /** * use blocks to draw each point, so data extents can be seen. */ public final static String VALUE_RENDER_TYPE_NNSPECTROGRAM="nnSpectrogram"; /** * draw events bars */ public final static String VALUE_RENDER_TYPE_EVENTS_BAR="eventsBar"; /** * values are drawn. */ public final static String VALUE_RENDER_TYPE_DIGITAL="digital"; /** * values are an RGB image, a rank 3 dataset [w,h,3] or [w,h,4]. The * "3" should be R,G, and B channels, and when "4" is used, ARGB is the * default. There can be a DEPEND_2 that is a QDataSet with ordinal data, * specifying the channels like so Ops.labelsDataset(['a','b','g','r']) or * Ops.labelsDataset(['a','b','g','r']). Only bgr or rgb models are supported * in the RGBImageRenderer, but future versions could support other color * models. */ public final static String VALUE_RENDER_TYPE_COMPOSITE_IMAGE="image"; /** * String, a java identifier that should can be used when an identifier is needed. This is * originally introduced for debugging purposes, so datasets can have a concise, meaningful name * that is decoupled from the label. When NAMEs are used, properties with the same * name should only refer to the named dataset. */ public final static String NAME="NAME"; /** * Boolean.TRUE indicates that the dataset is a "qube," meaning * that all dimensions have fixed length and certain optimizations and * operators are allowed. Note that when DEPEND_1 is a rank 1 dataset, * this implies QUBE. Likewise BUNDLE_1 is a qube. * Note the result of any slice must be a qube. */ public final static String QUBE="QUBE"; /** * String, representing the coordinate frame of the vector index. The units * of a dataset should be EnumerationUnits which convert the data in this * dimension to dimension labels that are understood in the coordinate frame * label context. (E.g. X,Y,Z in GSM.) * (Note this is before BUNDLE dimensions were formalized and is not used.) */ public final static String COORDINATE_FRAME="COORDINATE_FRAME"; /** * Map<String,Object> representing additional properties used by client codes. No * interpretation is done of these properties, but they are passed around as much * as possible. Note Object can be String, Double, or Map<String,Object>. METADATA_MODEL * is a string identifying the type of metadata, * a scheme for the metadata tree, such as ISTP-CDF or SPASE. */ public final static String METADATA="METADATA"; /** * String, a scheme for the metadata tree, such as ISTP or SPASE. This should identify * a node's type when the node is present, but should not require that the node * be present. When a required node is missing, this should be treated as if * none of the metadata is available. This logic is to support aggregating * metadata. */ public final static String METADATA_MODEL="METADATA_MODEL"; /** * the metadata is ISTP-CDF metadata */ public final static String VALUE_METADATA_MODEL_ISTP="ISTP-CDF"; /** * the metadata is SPASE (Space Physics Archive Search Extract) */ public final static String VALUE_METADATA_MODEL_SPASE="SPASE"; /** * the value is a complex number, having two elements, the first is real second is imaginary. */ public final static String VALUE_COORDINATE_FRAME_COMPLEX_NUMBER="ComplexNumber"; /** * String, human consumable identifying data version. Presently this * is intended for human consumption, but eventually we may make them usable * by software as well. Note if multiple versions go into making a product * (e.g. aggregation), the version string should contain space-delimited * version ids, so note versions must not contain spaces for other purposes. * Also two version strings containing the same value can be coalesced. If this * is prefixed with "<scheme>:", then this is to be interpreted as such: * otherwise it should be numerically sorted. * (see org.das2.fsm.FileStorageModel) */ public final static String VERSION="VERSION"; /** * String, Human-consumable string identifying the source of a dataset, such as the file or URI from * which it was read. Clearly this is easily lost as processes are applied to the * data, but when no other source is involved in a process (excluding library code * itself), then the source should be preserved. */ public final static String SOURCE="SOURCE"; /** * QDataSet of events scheme, containing a list of messages encountered during processing that annotate the data. * For example, the AggregatingDataSource in Autoplot would add an event to the dataset when a file could not be used. * This is a rank 2 dataset with BUNDLE_1=startTime,stopTime,message for now, but may soon allow for bounding qubes: * BUNDLE_1=startTime,stopTime,startEn,stopEn,message, and this should be visualized via the EventsRenderer. */ public final static String NOTES="NOTES"; /** Bundle Descriptor properties */ /** * String, the name of another dataset in the bundle descriptor. Before this was introduced, * a BundleDescriptor could have DEPEND_0 be a string. */ public final static String DEPENDNAME_0="DEPENDNAME_0"; /** * String, the name of another dataset in the bundle descriptor. Before this was introduced, * a BundleDescriptor could have DEPEND_1 be a string. Note this should only be used if * DEPEND_1 is rank 2, otherwise the dataset should be a property of DEPEND_1. */ public final static String DEPENDNAME_1="DEPENDNAME_1"; /** * String, the name of the rank 2 or more dataset in a bundle descriptor. */ public final static String ELEMENT_NAME="ELEMENT_NAME"; /** * String, the label of the rank 2 or more dataset in a bundle descriptor. */ public final static String ELEMENT_LABEL="ELEMENT_LABEL"; /** * int array, the dimensions of the element. A rank 0 is implicitly [], * a rank 1, n by 1, would be [1]. This is similar to the size command, for * one record of the data. * @see org.das2.qds.ops.Ops#size(org.das2.qds.QDataSet) */ public final static String ELEMENT_DIMENSIONS="ELEMENT_DIMENSIONS"; /** * Map<String,Object> representing additional properties used by client codes. No * interpretation is done of these properties, but they are passed around as much * as possible. The object values should be but don't have to be limited to: double, double array, * datum, QDataSet, String, String array. */ public final static String USER_PROPERTIES="USER_PROPERTIES"; /** * typical bin is min,max with min inclusive and max exclusive. */ public static String VALUE_BINS_MIN_MAX="min,max"; /** * scale type to suggest log axes and bins. */ public static String VALUE_SCALE_TYPE_LOG="log"; /** * scale type to suggest linear axes and bins. */ public static String VALUE_SCALE_TYPE_LINEAR="linear"; /** * the minimum length of each of the waveform packets in a rank 2 waveform dataset. */ public static int MIN_WAVEFORM_LENGTH=32; /** * the fill value often used in codes. */ public static double DEFAULT_FILL_VALUE= -1e31; /** * returns the rank of the dataset, which is the number of indeces used to access data. Only rank 0, 1, 2, 3, and 4 datasets * are supported in the interface. When a dataset's rank is 5 or greater, it should implement the HighRankDataSet interface * which affords a slice operation to reduce rank. * @return the rank, or number of indeces used to access data. */ int rank(); /** * rank 0 accessor. * @throws IllegalArgumentException if the dataset is not rank 0. * @return the value, see the property UNITS to interpret this. */ double value(); /** * rank 0 accessor which provides the string value * @throws IllegalArgumentException if the dataset is not rank 0. * @return the value, see the property UNITS to interpret this. */ String svalue(); /** * rank 1 accessor. * @param i the index * @return the value, see the property UNITS to interpret this. * @throws IllegalArgumentException if the dataset is not rank 1. */ double value( int i ); /** * rank 2 accessor. * @param i0 the index * @param i1 the index * @return the value, see the property UNITS to interpret this. * @throws IllegalArgumentException if the dataset is not rank 2. */ double value( int i0, int i1 ); /** * rank 3 accessor. * @param i0 the index * @param i1 the index * @param i2 the index * @return the value, see the property UNITS to interpret this. * @throws IllegalArgumentException if the dataset is not rank 3. */ double value( int i0, int i1, int i2 ); /** * rank 4 accessor. * @param i0 the index * @param i1 the index * @param i2 the index * @param i3 the index * @return the value, see the property UNITS to interpret this. * @throws IllegalArgumentException if the dataset is not rank 4. */ double value( int i0, int i1, int i2, int i3); /** * accessor for properties attached to the dataset. See final static members * for example properties. * @param name property name, such as "DEPEND_0" or "UNITS" * @return the value * @see #DEPEND_0 * @see #UNITS */ Object property( String name ); /** * accessor for properties attached to the dataset's first index. These properties * override (or shadow) properties attached to the dataset, and often implementations * will simply return the result of the no-index accessor. * * Note: properties of higher dimension are accessible only by slicing. * @param name property name, such as "DEPEND_0" or "UNITS" * @param i the index * @return the value * @see #DEPEND_0 * @see #UNITS */ Object property( String name, int i ); /** * return the length of the first dimension * @return the length of the first dimension */ int length( ); /** * return the length of the second dimension, for the ith element of the first dimension. Note * if there are zero elements in the first dimension, but this is a QUBE, then this should not * throw an IndexOutOfBoundsException. * @param i the index * @return the length of the second dimension at index i. */ int length( int i ); /** * return the length of the third dimension, for the ith element of the first dimension and jth element of the second dimension. * @param i the index * @param j the index * @return the length of the third dimension at index i. */ int length( int i, int j ); /** * return the length of the fourth dimension for the ith, jth and kth elements of the first three dimensions. * @param i the index * @param j the index * @param k the index * @return the length of the fourth dimension for the ith, jth and kth elements of the first three dimensions. */ int length( int i, int j, int k); /** * return a dataset that is a slice of this dataset, slicing on the zeroth * dimension. * A slice will be the elements at this index, for example if this dataset * is a rank 2 dataset flux(Time,Energy) then the slice of this will be * a rank 1 dataset flux(Energy). * The result of any slice will be a qube. * @throws IllegalArgumentException when dataset rank is zero. * @param i the index to slice at * @return the rank n-1 QDataSet at index i. */ QDataSet slice( int i ); /** * return a dataset that is a subset of this dataset. * For example: * 
     * {@code
     *    ds= DDataSet.createRank1(100);
     *    QDataSet trim= ds.trim(50,60);
     *    assert( trim.length()==10 );
     * }
     *
* @param start the first index to be included in the new dataset. * @param end the exclusive index indicating the last index. * @return a QDataSet with the same rank but fewer elements. */ QDataSet trim( int start, int end ); /** * return null or an object implementing the capability for the given interface * For example: *
     *ds= DDataSet.createRank1(100);
     *WriteCapability write= ds.capability( WriteCapability.class );
     *write.putValue( 99, -1e31 );
     *
* This allows operations to be performed efficiently. Note there is no WriteCapability class, this is * just an example. * * @param a capability * @param clazz the class, such as WriteCapability.class * @return the implementing class, or null (Jython None) if the capability is not provided. */ T capability( Class clazz ); }