.. -*- mode: rst -*-

.. _glossary:


Glossary
========

.. glossary::

**0xdata**
  Maker of H\ :sub:`2`\ O. Visit our website: http://0xdata.com

**binomial**
  a variable that takes on only the value 0 or 1. Binomial variables
  are often interpreted as 0 indicates that an event hasn't occurred
  or that the observation lacks a feature, where 1 indicates occurrence
  or display of an attribute.  

**categorical data or categorical variable**
  A qualitative variable (for example: blood type); (synonym for
  enumerator, factor).  

**cloud**
  (Synonym for cluster.)  See the definition of cluster. 

**cluster**
  1. (Synonym for cloud.)  A group of H\ :sub:`2`\ O nodes that work together; when a
  job is submitted to a cluster, all the nodes in the cluster work on
  a portion of the job. 

  2. in statistics: A cluster is a  group of
  observations from a data set that have been identified as 
  similar according to a particular clustering algorithm.

**continuous** 
  A variable that can take on all or nearly all values along an
  interval on the real number line. 


**CSV file**
  CSV is an acronym for comma separated value. A CSV file stores
  data in a plain text format. 

**destination key**   
  Automatically generated key for a model; it allows recall of a
  specific model later in analysis. Users can specify a
  different destination key than the key generated by H\ :sub:`2`\ O. 

**deviance** 
  Deviance is the difference between an expected value and an observed value. 
  It plays a critical role in defining GLM models. For a more detailed
  discussion of deviance please see the H\ :sub:`2`\ O Data Science documentation
  on GLM. 

**DKV**
  Distributed key/value store; see key/value store.

**family**
  In GLM family describes the options available for predictive
  modeling in GLM. Also see gaussian, poisson, gamma, binomial
   
**feature**
  Synonym for attribute, predictor, or independent variable. Usually
  the data observed on features are given in the columns of a data
  set.  

**gz (gzipped) file**
  Gzip is a type of file compression, a gzipped file is a file
  compressed by gzip.   

**HEX format**
  Records made up of hexadecimal numbers that represent machine
  language code or constant data. In H\ :sub:`2`\ O, data must be parsed into 
  .hex format before operations can be preformed on it.   

**instance**
  An instance of H\ :sub:`2`\ O occurs each time the user opens and runs H\ :sub:`2`\ O, and
  in the   process builds a cluster of nodes (even a one 
  node cluster on their local machine). The instance begins when the
  cluster is formed, and terminates when the program is closed 
  and the cloud is terminated.

**job**
  A piece of work that needs to be done. For example, reading
  in a data file, parsing a data file, or building a model. In the
  browser based GUI of H\ :sub:`2`\ O each job is listed in the admin menu under
  jobs. For more information see the user guide. 

**key**
  The .hex key generated when data are parsed into
  H\ :sub:`2`\ O. In the web based GUI "key" is an input on each page where users
  define models, and also any page where users validate models on a
  new data set or use a model to generate predictions.    

**key/value pair**
  A type of data that associates a particular key index to a
  certain datum.  

**key/value store**
  A tool that allows storage of schema-less data. Data usually
  consists of a string which represents the key, and the data itself
  which is the value.

**link function** 
  A user defined option in GLM. See the GLM user guide in Data Science
  for further detail. 

**n-folds** 
  User defined number of cross validation models generated by H\ :sub:`2`\ O

**node**
  In distributed computing systems nodes include clients,
  servers or peers. 
  
  In statistics a node is a decision or terminal point in a
  classification tree.

**parse**
  Analysis of a string of symbols or datum resulting in the
  conversion of a set of information from a person-readable
  format to a machine-readable format.

**seed**
  A starting point for randomization. Seed specification is used when
  machine learning models have a random component; it allows users to
  recreate the exact "random" conditions used in a model at a later
  time. 

**standardization**
  Transformation of a variable such that it is mean centered at 0 and
  scaled by the standard deviation.

**XLS file**
  A Microsoft Excel 2003 - 2007 spreadsheet file format. 

**Y**
  Dependent variable used in GLM; a user defined input selected
  from the set of variables present in the user's data.