Choosing the Right Model
Choosing between data storage models depends largely on the processing requirements outside of the chart. Within Objective Chart, the data access methods are basically the same.
The features of the three models are summarized in the table below. Blank cells in the table indicate that the model does not support that feature. Where relative evaluations are appropriate, the terms “Good – Better – Best” are used.
Table 18 – Data storage models
Required Feature | Std. | Dyn. | Struc |
Individually styled data items (highlight) | Yes | | |
Annotations for axis labels | Yes | O | O |
Annotations for feedback (chart tips) | Yes | O | O |
Null data flags for individual data values | Yes | | |
Hi-low histories | Yes | Opt. | |
Insert and delete data items | Yes | Hard | |
Data rolling | Best | Good | |
Fast access speed— large number of data items or rapidly changing values | Good | Best | Better |
Access to data in an external buffer | | | Yes |
Ease of use | Better | Good | Best |
O – requires override of GetAnnotations().
Hard – requires detailed knowledge
Opt. – optional, must be enabled
The Standard model has slower access speeds than the other models. However, the difference in performance is not large enough to be a deciding factor except in the most time-critical applications.
The Structure data model was given the highest rating for ease of use because the data values do not have to be assigned— they already exist.
Earlier Versions of Objective Chart
Early versions of Objective Chart required the use of SRDynamicGraph with the Dynamic and Structure data models. This is no longer the case and the standard SRGraph may be used if desired. SRDynamicGraph is retained for compatibility and may still be used.
Data stored using the Dynamic and Structure data models can not be copied into the Chart Wizard. The Wizard displays a default data set instead.
Chapter 14, “Objective Chart AppWizard,” contains a complete explanation.