Fundamental Building Blocks	Top

The Scheduler module performs Schedule Tasks on a recurring basis. A Schedule Task performs an operation on an SDI, such as adding Samples to the database. The SDI is the Scheduled Item.

Although you can build a Schedule Plan to accommodate almost any scheduling situation, the following example shows a logical use for a Schedule Plan, Folders, Sources, and Plan Items.

A recent taste test revealed that Reflux Springs should waste no time building the following scheduling strategy for water tests conducted at their wells:

In this case:

The Schedule Plan for Reflux could look something like this:

Schedule Plan: Add water samples Folder: 300-foot well    Plan Item: Add a water sample. Schedule it to be taken on June 10th.     Plan Item: Add a water sample. Schedule it to be taken on June 12th. Folder: 400-foot well   Folder: Container for the 400-foot sample    Plan Item: Add a water sample. Schedule it to be taken on June 15th.         Plan Item: Add a water sample. Schedule it to be taken on June 20th.

Each Plan Item indicates the Source of the sample, in this case the 300- or 400-foot well. You can choose any SDI as the Source of a Plan Item, or relate the Source to the Plan Item's Folder. More about this in the next section.

We demonstrate the interface for dealing with Folders and Plan Items in Creating Folders and Creating Plan Items. However, the following concepts are fundamental. You should not wait until you are staring at the interface to familiarize yourself with them.

Most scheduling applications would benefit from organizing Plan Items into Folders. Each of these child Folders would be the parent of their Plan Items (such as Well-300 is the parent of WaterSample-300-001 in the previous example).

When you add a Folder (covered in Creating Folders), you are offered the following choices that let you choose what the Folder represents:

Note the relationship between Folders and Sources:

The section below on Plan Items expands this concept.

If you want to use an SDI as a Source, you must enable the May Be Scheduled option in the SDC Definition Page. When you enable this option for an SDC, all SDIs for the SDC can be Sources.

Adding Plan Items (covered in Creating Plan Items) has subtle differences, depending on the the nature of the Folder to which you add them:

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When you add a Plan Item directly to the root node of the Schedule Plan (below left), or to a Folder that does not represent an SDI (below right), you must choose the Source (SDI that is associated with the Plan Item). Add to Root   Add to Folder that does not Represent an SDI Schedule Plan (root node)    Plan Item   Schedule Plan         Folder (non-SDI)    Plan Item After clicking Add Item, a new window opens, offering only one choice: Create Plan Items for source SDIs from SDC The SDI you choose here will be the Source for the Plan Item.

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When you add Plan Items to a Folder that represents an SDI (below), the Scheduler automatically uses that SDI as the Source for all Plan Items in the Folder. Add to Folder that Represents an SDI Schedule Plan         Folder (SDI)    Plan Item If you add a Plan Item to a Folder that represents an SDI, but the SDI no longer exists, the Scheduler interface informs you that the SDI no longer exists. It then removes the association between the Folder and the SDI, marks the folder with a black square, then treats the Folder as though it does not represent an SDI. The identifier of the SDI remains unchanged. You must rename it (as described in Creating Folders).

Scheduler Mechanics	Top

Before attempting to build a schedule or trying to interpret any of the information it reports, you must know how the Scheduler works. Behind the interface, the Scheduler uses separate engines to build and run the schedule:

From a configuration standpoint, note that the SchedulePlan SDC is a System SDC, i.e., it is extendable. The MaintenanceForm page for editing SchedulePlan SDCs can therefore be configured to show/hide these user columns.

To create Scheduled Events, the Event Scheduler uses information from both the Plan Items and the Schedule Plan. Here are simplified definitions (to be developed farther along in this discussion):

How the Event Scheduler creates Scheduled Events is probably best shown by example. We will use our previous Water Test Plan example, simplified to contain just one Folder and one Plan Item.

Plan with Folder   Plan Item Water Test Plan     Well-300            WaterSample-300-001

The Plan Item is set to AddSDIs as follows:

Before generating Scheduled Events to do this, the Scheduler needs to know the total time duration of the schedule. The Schedule Rule has told the Event Scheduler to add a WaterSample daily, but for how many days to you want this to occur? The Schedule Plan's Schedule Ahead value specifies this. In our example, the Schedule Plan is set as follows:

Each of these days in the Schedule defines an Event Date. In the example above, June 01 is the first Event Date, June 02 is the second Event Date, and so on.

When you view each Plan Item using the interface, the Plan Item reports details concerning the schedule. Continuing with our example:

If you do not want Scheduled Events generated for certain days, you can define a Schedule Exclude for the Schedule Plan. For example, if you want to generate Scheduled Events only for weekdays, you can setup a Schedule Exclude to skip all weekends. For simplicity, we have left this to be discussed later in the interface description (see Excluding Events).

It is now worth mentioning that you must turn on the Schedule Plan, Folder, and Plan Item in order for the Event Scheduler to do anything. Don't worry about this now (it is covered later in Status).

Also worthy of mention is the Polling Interval. This determines the exact time Scheduled Events are generated. Since this does not affect construction of the schedule, we defer discussion to the section on Polling.

Trying to leave nothing to chance, this is also a good time to mention that you will be locked out of the Scheduler unless you set your timeouts accordingly. We defer this discussion to the section on Timeout Poll Interval.

After Scheduled Events have been generated, the Task Executor runs the Schedule Tasks for each Event.

The Plan's Execute Ahead determines how far in advance to schedule all Schedule Tasks in the Schedule Plan. Extending our example, the Schedule Plan is set as follows:

Not to add unnecessary complexity here, but this one caught me off guard when I was trying to figure out how all of this worked.

In the previous examples, the time specified by the Start Date was earlier than that specified by the Schedule Rule. Recall that on June 1st, we generated our Scheduled Events at 2 p.m., with the Schedule Rule specifying "daily at 6 p.m". I found that if the time specified by the Start Date is later than that specified by the Schedule Rule, you will see something subtly different. Assume everything in the previous example is the same, but your Schedule Rule says "Every Day @ 06:00". At the Start Date, the Scheduler generates an extra Event for the first day of the schedule, and executes it ahead of schedule.

Both the Event Scheduler and the Task Executor constantly poll (query) the SchedulePlanItem table to determine if any Events must be generated or any Tasks are scheduled to be run. You can set the polling interval using the Schedule Poll Interval property in System Tools.

It follows that neither the Event Scheduler nor the Task Executor do anything until the next polling interval following the time specified by the Start Date. For example, if your polling interval is set for 60 seconds, and the Start Date is June 01 at 14:00, the Scheduled Events will actually be generated within a 60-second period after 14:00 (whenever the next 60-second polling interval begins). This is really not an issue, since the exact time Events are generated is of little consequence when generating a schedule... it is the Execute Date that tells users when to take action. If you want to generate Events more quickly, you can decrease your Schedule Poll Interval; however, this makes your machine work harder.

When you access a Schedule Plan or Plan Item, LabVantage locks all data associated with it. When locked, no other user can access these data.

Following a successful logon, LabVantage assigns each user a Connection Id. This unique identifier is held in the Connection table of the LabVantage schema. The Timeout Poll Interval properties in System Tools monitor the Connection Id, performing various functions if configurable periods of time expire. One of these properties affects data locking:

Assume you set this for 3600 seconds. If you create a Schedule Plan with some Plan Items, and do not modify them, they will be unlocked after one hour.

You can set the Status of any Schedule Plan, Folder, and Plan Item to On or Off. The following information describes this behavior.

You can turn a Schedule Plan on or off only in the Schedule Plan List Page (shown later in the section on Creating Plans).

The Status information below applies to all Folders whether or not they represent SDIs. Turning a Folder on or off also turns all of its child Folders on or off, respectively.

In the nodes of the Schedule Plan tree, Status behaves according to the rules below. A Status of N/A means the Status does not matter (it can be either on of off).

1.	Turning off a parent prevents all of its children from generating Scheduled Events.
	Example 1 Turning off the root node Plan-001 prevents all Plan Items from generating Scheduled Events. Schedule Plan Tree   Status   Scheduled Events Generated? Plan-001   Off     Folder-A   N/A     PlanItem-003   N/A   No PlanItem-004   N/A   No Folder-B   N/A       Folder-C   N/A           PlanItem-008   N/A   No       PlanItem-009   N/A   No Example 2 Folder-A and Folder-C are off. Consequently, their PlanItems cannot generate Scheduled Events. Schedule Plan Tree   Status   Scheduled Events Generated? Plan-001   On     Folder-A   Off     PlanItem-003   N/A   No PlanItem-004   N/A   No Folder-B   On       Folder-C   Off           PlanItem-008   N/A   No       PlanItem-009   N/A   No
2.	You can selectively turn Plan Items on and off. Those that are on will generate Scheduled Events if their parent nodes are on.
	Example Schedule Plan Tree   Status   Scheduled Events Generated? Plan-001   On     Folder-A   On     PlanItem-003   Off   No PlanItem-004   On   Yes Folder-B   On       Folder-C   On           PlanItem-008   Off   No       PlanItem-009   On   Yes