datahub/library-model.markdown

layout, title

layout	title
container	Models and Backends

Models and Backends

Models help you structure your work with data by providing some standard objects. The key ones are Dataset and Record -- a Dataset being a collection of Records. Additionally, there is a a Field object for describing the columns of a Dataset, a Query object for describing queries, and a Facet object for holding summary information about a Field (or multiple Fields).

Models

Dataset

A Dataset is the central object in Recline. It has the following key attributes:

• currentRecords: a collection of Records currently loaded for viewing (updated by calling query method) - note that this need not be all the records in the dataset (for example, you may have connected to a source where the complete dataset contains a million records but you have only loaded a 1000 records)
• fields: (aka columns) is a Backbone collectoin of Fields listing all the fields on this Dataset (this can be set explicitly, or, will be set by Dataset.fetch()
• docCount: total number of records in this dataset
• backend: the Backend (instance) for this Dataset.
• queryState: a Query object which stores current queryState. queryState may be edited by other components (e.g. a query editor view) changes will trigger a Dataset query.
• facets: a collection of Facets

Record (aka Row)

A Record represents a single entry or row in a dataset. As Record fits very nicely with the default behaviour of a Backbone Model object it has little additional functionality.

Field (aka Column)

A Field should have the following attributes as standard:

{% highlight javascript %} var field = new Field({ // a unique identifer for this field- usually this should match the key in the records hash id: 'my-field-id' // (optional: defaults to id) the visible label used for this field label: 'My Field Name', // (optional: defaults to string) the type of the data in this field. // Should be a string as per type names defined by ElasticSearch - see // Types list on http://www.elasticsearch.org/guide/reference/mapping/ type: 'string', // (optional - defaults to null) used to indicate how the data should be formatted. See below. format: null, // (default: false) attribute indicating this field has no backend data but is just derived from other fields (see below). is_derived: false {% endhighlight %}

Rendering, types and formats

One can customize the rendering of fields in the user interface and elsewhere by setting a renderer function on the field. You do this by setting a field attribute:

{% highlight javascript %} myfield.renderer = myRenderFunction; {% endhighlight %}

Your renderer function should have the following signature:

  function(value, field, record)

where value is the value of this cell, field is corresponding field object and record is the record object (as simple JS object). Note that implementing functions can ignore arguments (e.g. function(value) would be a valid formatter function).

To guide the behaviour of renderers we have type and format information. Example types and formats are:

• type=date, format=yyyy-mm-dd
• type=float, format=percentage
• type=string, format=markdown (render as markdown if Showdown available)

Default renderers are provided - see the source for details, but a few examples are:

• type = string
  • no format provided: pass through but convert http:// to hyperlinks
  • format = plain: do no processing on the source text
  • format = markdown: process as markdown (if Showdown library available)
• type = float
  • format = percentage: format as a percentage

Derived fields:

• deriver: a function to derive/compute the value of data in this field as a function of this field's value (if any) and the current record. It's signature and behaviour is the same as for renderer. Use of this function allows you to define an entirely new value for data in this field. This provides support for a) 'derived/computed' fields: i.e. fields whose data are functions of the data in other fields b) transforming the value of this field prior to rendering.

Query

Query instances encapsulate a query to the backend (see query method on backend). Useful both for creating queries and for storing and manipulating query state - e.g. from a query editor).

Query Structure and format

Query structure should follow that of ElasticSearch query language.

NB: It is up to specific backends how to implement and support this query structure. Different backends might choose to implement things differently or not support certain features. Please check your backend for details.

Query object has the following key attributes:

• size (=limit): number of results to return
• from (=offset): offset into result set - http://www.elasticsearch.org/guide/reference/api/search/from-size.html
• sort: sort order - http://www.elasticsearch.org/guide/reference/api/search/sort.html
• query: Query in ES Query DSL http://www.elasticsearch.org/guide/reference/api/search/query.html
• filter: See filters and Filtered Query
• fields: set of fields to return - http://www.elasticsearch.org/guide/reference/api/search/fields.html
• facets: specification of facets - see http://www.elasticsearch.org/guide/reference/api/search/facets/

Additions:

• q: either straight text or a hash will map directly onto a query_string query in backend

• Of course this can be re-interpreted by different backends. E.g. some may just pass this straight through e.g. for an SQL backend this could be the full SQL query

• filters: array of ElasticSearch filters. These will be and-ed together for execution.

Examples

{
   q: 'quick brown fox',
   filters: [
     { term: { 'owner': 'jones' } }
   ]
}

Facet – Store summary information (e.g. values and counts) about a field obtained by some 'faceting' or 'group by' method

Structure of a facet follows that of Facet results in ElasticSearch, see: http://www.elasticsearch.org/guide/reference/api/search/facets/

Specifically the object structure of a facet looks like (there is one addition compared to ElasticSearch: the "id" field which corresponds to the key used to specify this facet in the facet query):

{
  "id": "id-of-facet",
  // type of this facet (terms, range, histogram etc)
  "_type" : "terms",
  // total number of tokens in the facet
  "total": 5,
  // @property {number} number of records which have no value for the field
  "missing" : 0,
  // number of facet values not included in the returned facets
  "other": 0,
  // term object ({term: , count: ...})
  "terms" : [ {
      "term" : "foo",
      "count" : 2
    }, {
      "term" : "bar",
      "count" : 2
    }, {
      "term" : "baz",
      "count" : 1
    }
  ]
}

Backends

1. Data is held in an in memory store on the Dataset object.
2. Data is transparently sourced from a backend store.