====Row Based vs Column Based Drivers====

Some data sources have the option of performing either //row based// or //column based// lookups.

===Row Based Drivers===

A row-based driver is designed for the situation where all of your information is stored in a single table, and one column contains an identifier for that information. Each row will have a minimum of....

^Column Name^Purpose^
|Lookup Column|The name of this measurement channel|
|Value|The value of that measurement|
|Timestamp //(optional)//|The date and time of the measurement|

So for example, in the following example...

^Timestamp^Name^Value^
|12:42|Temperature 1|25.4|
|12.42|Temperature 2|13.2|
|12.33|Temperature 1|24.4|

In this case, the lookup value you assign to each data-binding in ARDI will be the value contained in that 'lookup' column.

The **lookup** is 'Name'. So points in ARDI would simply be connected to 'Temperature 1' and 'Temperature 2'.

===Column-Based Drivers===

In column-based drivers, the data source has several columns per row, and the lookup from ARDI is actually the //column name//. 

They usually have a minimum of....

^Column Name^Purpose^
|Timestamp|The date and time of the measurement|
|Value A|The value of channel A|
|Value B|The value of channel B|
|Value C|The value of channel C|

^Timestamp^TMP1^TMP2^
|12:42|25.4|13.2|
|12.33|24.4|11.5|

In this case, the ARDI lookup is the name of the channel. IE. "TMP1" or "TMP2".

===Keyed Column-Based Drivers===

Some select drivers (for instance, our Oracle driver) can support a //key// on a column-based driver. In fact, they may even support **multiple** keys. 

These work like a hybrid between the two - they are given two lookup values for each data-binding - the //lookup// and the //column//.

As an example, take the following...

^Timestamp^VEHICLE^ENGINETMP^OILTMP^
|12:42|1|25.4|13.2|
|12:42|2|25.4|13.2|
|12.33|1|24.4|11.5|
|12:33|2|25.4|13.2|

In this case, the lookup for engine temperature on vehicle 1 would be....

|Lookup|1|
|Column|ENGINETMP|

//History lookups on these drivers can be quite expensive//

===Multi-Keyed Column-Based Drivers===

These are the same as keyed column based drivers, but with the addition of multiple keys.

As an example, take the following...

^Timestamp^VEHICLE^OWNER^ENGINETMP^OILTMP^
|12:42|1|1|25.4|13.2|
|12:42|2|1|25.4|13.2|
|12.33|1|1|24.4|11.5|
|12:33|2|2|25.4|13.2|

In this case, the lookup for engine temperature on vehicle 2 with owner 1 would be...

|Lookup|2,1|
|Column|ENGINETMP|

This would fetch the //second// record as the active, live data.

//History lookups on these drivers can be **extremely** expensive//