The meta informations about an HPLC-MS experiment are stored in ExperimentalSettings and SpectrumSettings. All information that is not covered by these classes can be stored in the type-name-value data structure MetaInfo. All classes described in this section can be found in the METADATA folder.

MetaInfo

DataValue is a data structure that can store any numerical or string information. It also supports casting of the stored value back to its original type.

MetaInfo is used to easily store information of any type, that does not fit into the other classes. It implements type-name-value triplets. The main data structure is an associative container that stores DataValue instances as values associated to string keys. Internally, the string keys are converted to integer keys for performance reasons i.e. a map<UInt,DataValue> is used.

The MetaInfoRegistry associates the string keys used in MetaValue with the integer values that are used for internal storage. The MetaInfoRegistry is a singleton.

If you want a class to have a MetaInfo member, simply derive it from MetaInfoInterface. This class provides a MetaInfo member and the interface to access it.

The classes involved in meta information storage

The following example (Tutorial_MetaInfo.cpp) shows how to use Metadata. We can simply set values for the string keys, and setMetaValue registers these names automatically. In order to access the values, we can either use the registered name or the index of the name. The getMetaValue method returns a DataValue, which has to be casted to the right type. If you do not know the type, you can use the DataValue::valueType() method.

Int main()
{
  MetaInfoInterface info;
  //insert meta data
  info.setMetaValue("color", String("#ff0000"));
  info.setMetaValue("id", 112131415);
  //access id by index
  UInt id_index = info.metaRegistry().getIndex("id");
  cout << "id   : " << (UInt)(info.getMetaValue(id_index)) << endl;
  //access color by name
  cout << "color: " << (String)(info.getMetaValue("color")) << endl;
  return 0;
} //end of main

Meta data of a map

This class holds meta information about the experiment that is valid for the whole experiment:

sample description
source files
contact persons
MS instrument
HPLC settings
protein identifications

Map meta information

Meta data of a spectrum

This class contains meta information about settings specific to one spectrum:

spectrum-specific instrument settings
source file
information on the acquisition
precursor information (e.g. for MS/MS spectra)
product information (e.g. for SRM spectra)
processing performed on the data
peptide identifications

Spectrum meta information

Meta data associated to peaks

If you want to annotate the peaks or raw data points in your spectra with meta information, there are three different ways to do this with different advantages and disadvantages.

If each peak is annotated with the same type of information (e.g. width of a peak):

Use the meta data arrays provided by MSSpectrum (recommended)
- Advantages: Independent of peak type, information automatically stored in mzML files
- Disadvantages: Information can be accessed through index only
Derive a new peak type that contains members for the additional information
- Advantages: Very fast
- Disadvantages: Information not automatically stored in mzML files, Custom peak type are not supported by all algorithms

If you need to annotate only a small subset of the peaks with meta information:

Use the MetaInfoInterface of RichPeak1D
- Advantages: Each peak can be annotated with individual information
- Disadvantages: Quite slow, Information not automatically stored in mzML files