Internally the classic engine uses a set of report-states to process a report. Each report state captures all variables and object states of a particular process state. The report processing always starts with a BeginReport-State and ends with a ReportFinishedState. Each state is independent and allows to suspend and restart the report processing at a later time.

Understanding the report-state and its state-transitions is crucial to understand how the reporting engine processes the data and generates the events that drive the report content generation. Some events can spawn subreport processes if the corresponding root-level band contains subreports as childs.

Banded report processing

BeginReport

The BeginReport state initializes the report processing, queries the data and activates all functions for the report. The state fires the report-initialized event to all functions to inform the functions that a new report processing run has started.

Previous states
Next state	ReportHeader
Event	reportInitialized(..)
Subreports

ReportHeader

The report header state is responsible for printing the report header. The state fires the report-started event to all functions.

If the first group of the report is a crosstab-group, this state transitions into a BeginCrosstabState next, otherwise it continues as BeginGroup state.

Previous states	BeginReport
Next state	BeginGroup, BeginCrosstab
Event	reportStarted(..)
SubReports	on ReportHeader

BeginGroup

Activates a group. Every report is guaranteed to have at least one group. A group is defined as "consecutive set of rows, which have the same values in the columns specified by the group's arguments". Groups are formed by specifying grouping arguments; usually the name of one or more columns; that control which rows contain into a given group instance. Groups can be nested into each other. On nested groups, each subgroup automatically inherits the grouping arguments of their parent groups. Therefore a group is considered finished if either the values of the group arguments change or if one of the parent groups is finished.

If the current group of the state is not the inner most group, the state will transition into another BeginGroup-state. If the next group is a crosstab-group, the state continues with a BeginCrosstab-state. Once all groups are opened, the processing continues with the BeginDetails-state.

Previous states	ReportHeader, BeginGroup, JoinEndGroup
Next state	BeginGroup, BeginDetails, BeginCrosstab
Event	groupStarted(..)
SubReports	on GroupHeader

BeginDetails

This state starts the details-processing. During the processing, the layouter will print the details-headers and prepares the details-footers. If the main datasource of the report is empty, this state will trigger the printing of the no-data-band.

If the main datasource is empty, this state transitions into a EndDetailsState immediately.

Previous states	BeginGroup
Next state	ProcessDetails, EndDetails
Event	itemsStarted(..)
SubReports	on NoDataBand if the data-source is empty

ProcessDetails

This state processes the itemband. The reporting engine's state processing generates a process-details state for each row in the report's data-source. If the data-source is empty, no such state is generated. Therefore reports with no rows in the report's datasource will generate all group-headers and footers but will not produce any itembands.

Previous states	BeginDetails
Next state	JoinDetails
Event	itemsAdvanced(..)
SubReports	on ItemBand

JoinDetails

This state post processes the itemband. If the current group is not finished, it advances the internal cursor to the next row of data, otherwise it delays the advance operation until all group-footers have been printed.

This state is an artificial state and therefore it generates no events. If the current group is not finished, this state transitions into a new ProcessDetails-state, otherwise the details section is finished by transitioning into a EndDetails-state.

Previous states	ProcessDetails
Next state	ProcessDetails, EndDetails
Event
SubReports

EndDetails

The EndDetails state signals the end of the details section processing and triggers the printing of the details-footer.

Previous states	BeginDetails, JoinDetails
Next state	EndGroup
Event	itemsFinished(..)
SubReports

EndGroup

The EndGroup state finishes the current group. It triggers the printing of the group-footer and closes the group's instance. This state unconditionally transitions into a JoinEndGroup state.

Previous states	EndDetails, JoinEndGroup, JoinCrosstab
Next state	JoinEndGroup
Event	groupFinished(..)
SubReports	on GroupFooter

JoinEndGroup

This is another artificial state to simply the report processing. If the report has reached the end of the data-source or if the parent group is finished as well, this state transitions into a new EndGroup state to finish the parent group. Otherwise, if the report contains more data, this state continues as BeginGroup state.

Previous states	EndGroup
Next state	ReportFooter, EndGroup, BeginGroup
Event
SubReports

ReportFooter

This state fires the reportFinished event to inform all functions that the report processing is going to end soon. This also triggers the printing of the report footer.

Previous states	JoinEndGroup
Next state	EndGroup, BeginGroup, BeginCrosstab
Event	reportFinished
SubReports	on ReportFooter

ReportDone

This state fires the reportDone event, which is a global signal for all functions to clean up their internal state as the reporting ends now. Depending on whether the current report is a master report or a subreport, this state transitions into either a EndReport or EndSubreport state.

In the old days, this event was used to postprocess the report footer for the final printing, but as of 0.8.9 this part of the event processing is disabled and has no effect in the current layouting system.

Previous states	ReportFooter
Next state	EndReport, EndSubReport
Event	reportDone
SubReports

EndSubReport

This state merges the subreport processing with the parent report-state. The state will transform into a copy of the stored parent state to continue the report processing where the subreport process interrupted it.

Previous states	ReportDone
Next state	any state able to spawn subreports
Event
SubReports

EndReport

This state is a artificial state to allow the report processor to detect that the report processing has finished. The state does nothing and any attempt to advance the state into something else will produce errors.

Previous states	ReportDone
Next state
Event
SubReports

Crosstab report processing

BeginCrosstab

BeginOtherAxis

BeginRowAxis

BeginColumnAxis

BeginFact

ProcessFact

JoinFact

EndFact

EndColumnAxis

JoinEndColumnAxis

EndRowAxis

JoinEndRowAxis

EndOtherAxis

JoinEndOtherAxis

EndCrosstab

JoinEndCrosstab

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