/ Layouts / Chapter 49. Charts

Groups of data and data series

One of the most important characteristics of any chart is a table of data on the basis of which a chart is built. Any cataloged query (but not the table itself and not a browsed non-cataloged query) can be used in ObjectLand for this purpose.

As it is well known, both tables and queries are rectangular (two-dimensional) arrays of data consisting of rows (records) and columns (fields). To build a chart one or several one-dimensional numeric arrays – groups of data, are used. ObjectLand allows using either the query column (that is, the value of one of numeric fields for all query records) or the query row, to be more exact – numeric fields of one query record (non-numeric fields are ignored) as groups of data. A chart displays every group of data in a graphic form convenient for visual comparison of data elements from this group (for example, in the form of a set of multicolored columns).

In the case if several groups of data are specified, analogous elements from different groups form data series. The user can visually compare values of different elements of data of one series (for example, compare columns of one color from several groups by height).

Notions of a group of data and data series are complementary: if query columns (fields) are used as groups of data, query rows (records) will comprise data series. And on the contrary, if groups of data are formed by records, then data series are formed by fields.

The user has a possibility to select particular numeric query fields which should be used when building a chart, however, he cannot choose particular records. All query records are always used in the chart, and if some records are unnecessary it is required to change the condition of forming a query.

Generally, if none of the existing queries is right for building the required chart, a natural solution is creating a new cataloged query meant especially for building the present chart.

As an example charts built on the basis of a cataloged query “Allocation of Inhabitants by Streets” which is part of GDB “City” can be examined. This small query is presented in table 49-1. It contains names of twelve streets, number of inhabitants in every street and the average number of inhabitants (that is, the total number of inhabitants divided by the number of buildings) for every street. You shouldn't be surprised that the average number of inhabitants is less than 1 – it just means that this street also has uninhabited buildings.

Table 49-1. Query “Allocation of Inhabitants by Streets”

The layout at figure 49-1 contains two charts built by this query.

Figure 49-1. Charts by query “Allocation of Inhabitants by Streets”

The upper chart contains two groups of data displayed as circles divided into multicolored sectors. These groups correspond to numeric fields “Total inhabitants” and “Average number of inhabitants”. The number of sectors (and number of data series) is equal to the number of records in the query. On every sector its numeric value is shown (in this case percentage value). To the right a legend is located. It explains the correspondence between street names and color of the appropriate data series.

The bottom chart displays twelve groups of data (by the number of records in the query), but each group consists of two values. Thus, there are two data series, sectors of green color correspond to one series, sectors of black one – to the other. It is seen from the legend that these data series correspond to numeric query fields.

We do not consider the question if it is wise enough to display such different values as the total number of inhabitants and their average number in the form of sectors of one circle. This example is of illustrative value.