Fault Tree Diagram

This is the workspace where the Fault Trees are developed and the user can interact with them.

Diagram Actions

Switch to another system

The first dropdown of the top-left, which shows the name of the loaded system, lists the systems of every project the user can see, grouped under the name of their project. Clicking on a system loads its Fault Tree without going back to the home page.

• The loaded system is highlighted in the list, the same way as the loaded Fault Tree in its own dropdown.

• When the dropdown opens, the list scrolls to the loaded system.

Select a Fault Tree to be displayed in the diagram

The two dropdowns on the top-left, each one with its title on its left, choose what the diagram shows:

• System: the system open. It lists the systems the user can see, under the name of their project. Choosing one opens its fault tree without going back to the home page.

• Top Event: the Fault Tree of the system shown in the diagram, by the ID of its top gate.

Search a node in the diagram

The magnifying glass of the top-right searches a node in the different Fault Trees of the system. Clicking on it opens a text-box and, under it, the list of the nodes of the system, the same list as the one of the ID of a new child.

• The nodes are grouped by Fault Tree, under the ID of its Top Gate and the number of its nodes. Each Fault Tree starts with its Top Gate.

• Each node shows its ID, its parent and its description. The parent tells apart the copies of a node.

• On its left, each node shows the colour of its type in the diagram: AND gate, OR or Vote gate, Transfer gate or primary event. The repeated primary events have the colour of the other primary events.

• Writing in the text-box keeps only the nodes whose ID or description contains the text written, which is highlighted.

• Clicking on a node, or pressing Enter, moves the diagram to the node and highlights it. If the node is in another Fault Tree, that Fault Tree is loaded first, and if it is inside a Transfer Gate, the diagram goes inside it. The Top Event dropdown shows the Fault Tree of the node.

• Enter and Go choose the node marked in the list: the one whose ID is the text written, or else the first one of the list. The arrows Up and Down move the mark, and Esc closes the list.

Maximize the diagram

To maximize the diagram and make it easier to read, press CTRL+M. To return, press CTRL+M again.

Add New Top Gate

The Top Gate is the gate where the breakdown analysis starts to develop. It gives the Unavailability of the system analyzed.

To add a new Top Gate, click on New top event > AND Gate, New top event > OR Gate or New top event > Vote Gate to insert it as an AND, an OR or a Vote gate.

Note

When the Top Gate is created as a Vote gate, Robin asks for the value of the threshold K after the ID and the Description have been introduced. See the Computation section.

After clicking on the button, a new Top Gate will be created with a generic ID and Description.

Center Top Gate in the diagram

Click the icon and the top gate will be centered in the diagram

Undo and Redo Functionality in the diagram

How to Use Undo and Redo

Undo: To revert the most recent action, you can click on the undo icon in the toolbar. Alternatively, you can use the keyboard shortcut CTRL+Z.

Redo: To reapply an action that you’ve undone, click on the redo icon in the toolbar. The keyboard shortcut for this function is CTRL+Y.

An “action” refers to any modification made to the nodes within the diagram (i.e: add a child node, change a node parameter, delete a node, etc.)

Right-Click actions

A. Add Child

Nodes can be added directly with this right click option. Detailed explanation is in Node Actions section. Detailed information about add child is handled in the section Node Actions

B. Switch On/Off

Switch Off: It changes the selected node and its children nodes in switch-off status

Switch On: It changes the selected node and its children nodes in switch-on status

C. Comment

The user can add/edit/see/delete the comment of a node.

It can be done through a modal directly or being redirected to another page where comments are handled

Below image is showing the add comment modal

D. Copy/Cut/Paste

Copy: When a user uses the “Copy” function, a duplicate of the selected node along with its child nodes is created. The original node and its child nodes remain unchanged in their original location. This is essentially a non-destructive operation that leaves the original structure intact. It can also be used by the keyboard shortcut CTRL+C

Cut: When a user uses the “Cut” function, removes the selected node and its child nodes from their current location while storing them temporarily so they can be pasted elsewhere. This is a destructive operation that alters the original structure by removing the selected nodes. It can also be used by the keyboard shortcut CTRL+X

Paste: It attaches the previously copied or cut nodes, along with their respective child nodes, to a different target node. This allows you to effortlessly move or duplicate complex node structures within the system, preserving their internal relationships. It can also be used by the keyboard shortcut CTRL+V

E. Delete

When a user deletes a node, from the Delete button of the node, the right-click menu or the Del key, a modal is displayed to confirm it.

For a gate (AND, OR, Vote or Transfer gate), the modal offers Delete and Cancel. Delete removes the gate and every node hanging from it from the fault tree, and from every repetition of its parent. When the gate is repeated in the project and a copy of it remains below another gate, nothing else is lost. When it is the last copy, the gate and its children are deleted from the database for good, which cannot be undone: the modal warns about it before going on. A Transfer Gate keeps the branch it folds, so Delete removes that branch too, and the Transfer Gate counts as a copy of the gate it folds. When several nodes are selected and one of them is a gate, the modal is the same, and the warning names the gates deleted for good.

For the rest of the nodes (basic events, undeveloped events and remarks), the user needs to choose the delete-option:

1. Delete from DB: The node is deleted both in the fault tree and in the database.

2. Delete: The node is deleted only from the tree and deleted node information can be used anytime.

When a basic or undeveloped event is also used below another gate, in this fault tree or in any other fault tree of the project, the modal only offers Delete and Cancel: the event is removed from here, and the other copy keeps it in the project, so there is nothing to keep in the database.

F. Move left/right

This function is used to change the position of the node among sibling nodes.

It can also be used by the keyboard shortcut CTRL+Left/Right

G. Transfer Gate

Users can perform transfer gate related actions with right click.

Detailed explanation about its functionality can be found in the section of Node Actions

H. Send as TG (New FT)

This option allows user to create a new Fault Tree with the selected node as top gate

I. See related parents

This option allows user to see related parent nodes information in a modal.

J. Hide/Show Node (print)

This option leaves the selected node out of the printed diagram, or puts it back in. It changes nothing else: every calculation keeps taking the node into account. See Hide Nodes in the Print.

Node Actions

Clicking on a node will display the different actions available with that node. Different actions can be executed depending on the type of node.

AND/OR gate actions

For AND and OR Gates, the actions available to be performed are the following:

• Change information

By clicking Change information, the ID and the Description of the gate can be changed. Click on Confirm changes to save the changes.

• Change the type of gate

By clicking Change to AND gate or Change to OR gate, the type of gate will be transformed from an AND gate to an OR gate and viceversa.

An AND or an OR gate can also be converted into a Vote gate by clicking Change to VOTE gate. Since a Vote gate needs a threshold, Robin opens the Vote Threshold (K-of-N) dialog to introduce the value of K before applying the change. The dialog limits the value to the number of children the gate currently has.

Note

The conversion works in both directions: a Vote gate offers the Change to AND gate and Change to OR gate actions, which discard its threshold.

• Change K (vote)

This action is only available on Vote gates. It reopens the Vote Threshold (K-of-N) dialog to modify the value of K without having to recreate the gate.

Note

Changing the type of a gate or the value of K invalidates the results already computed, so the fault tree has to be recalculated. See Computation for the logic applied by each gate.

• Add a node

By clicking Add child, a new node can be inserted as a child of the selected node. There are different types of nodes that can be added (AND, OR, Vote, Basic, Undeveloped, Transfer and Remark).

Note

When the type selected is Vote Gate, the form shows an additional field K (vote threshold). If it is left empty, Robin asks for the value of K in a dialog after clicking Create node.

When an existing Vote gate is inserted by introducing its ID, the K field is filled in with the threshold of that gate and cannot be edited, since both occurrences are the same node.

Choosing an existing node

The ID field is used both to give an ID to a new node and to insert a node that already exists in the project. Once the type of node is selected, clicking the field unfolds the list of the nodes of that type that already exist in the project:

• The nodes are grouped by system. The name of each system is shown on top of its nodes, together with the number of nodes it has, and stays visible while scrolling through them.

• Each node is shown with its ID and, below it, its description.

• The IDs are sorted in natural order, so BE-2 comes before BE-10.

Typing in the field filters the list while writing: only the nodes whose ID contains the text typed are kept, in upper or lower case, and the matching part of each ID is highlighted. The systems left without nodes are hidden.

A node can be chosen in two ways:

• With the mouse: click on it.

• With the keyboard: move through the list with the ↑ and ↓ arrow keys and press Enter. If the ID typed is exactly the ID of an existing node, that node is already selected and Enter chooses it directly.

Choosing a node inserts that node instead of a new one: its ID is written in the field and the rest of the fields are completed with its information. Esc closes the list without choosing anything. If the ID typed does not match any node, the list shows No existing node matches, and a new node is created with that ID.

A Basic or Undeveloped event can be chosen this way before selecting a calculation model, since an existing event brings its own. A new event needs its model to be selected before it can be created.

When the project has many nodes, the list shows them 200 at a time. A line at the end of the list indicates how many are shown out of the total. Scrolling down to the end of the list, or going past the last node with the ↓ arrow key, loads the next 200. Typing part of the ID narrows the list down and is usually the fastest way to find a node.

Note

For AND/OR gates, if the ID of an existing gate in the same project is introduced, the fields are completed with the information of the gate and the complete branch including all its children gates will be inserted.

Click Create node to add the node.

See Computation for more information about the parameters of the primary events.

• Show as transfer gate

The AND/OR gate branches can be broken into transfer gates to to facilitate the reading of the Fault Tree.

By clicking Show as transfer, the branch will be substituted by a transfer gate node.

• Send as a Top Gate (New FT)

By clicking Send as a Top Gate (New FT), the complete branch will be copy as a new Fault tree being the node the new top gate.

• Delete a node

By clicking Delete, the node and all its children will be removed.

Transfer gate actions

For Transfer gates, the actions available to be performed are the following:

• Change Description/ID

By clicking Change Description/ID, the ID and the Description of the gate can be changed. Click on Confirm changes to save the changes.

• Go inside the Transfer Gate

By clicking Go inside the Transfer Gate, the branch of the transfer gate will be shown as a different Fault tree. This branch can be modified as a usual Fault Tree.

In the top of the diagram, the button Go Back will appear to collapse the transfer gate diagram and return to the original Fault Tree. Also, the transfer gate diagram’s top node will have this button available as an option. Meanwhile the Top Event dropdown shows the original Fault Tree, and it cannot be changed until Go Back.

• Undo transfer gate

By clicking Undo transfer gate, the transfer gate will be replaced by the original branch.

• Send as a Top Gate (New FT)

By clicking Send as a Top Gate (New FT), the complete branch will be copy as a new Fault tree being the node the new top gate.

• Delete a node

By clicking Delete, the node and all its children will be removed.

Basic/Undeveloped Events

For Basic and Undeveloped Events, the actions available to be performed are the following:

• Change Parameters

By clicking Change parameters, the ID, the Description, the type of probability and the parameters related with the probability can be changed. Click on Confirm changes to save the changes.

For a Basic Event, the ID field also offers the other Basic Events that already exist in the project, with the same list used to add a child (see Choosing an existing node). Clicking the field unfolds the whole list, grouped by system, even though the field already holds the ID of the event; typing filters it. The event being edited is not in the list.

Choosing an event of the list turns the edited event into one more copy of the chosen one: its ID is written in the field and the Description, the type of probability and its parameters are completed with the information of the chosen event. The copy always keeps the values of the chosen event, so those fields are disabled. Events of any system of the project can be chosen. Click Confirm changes to save it, or Cancel to leave the event as it was.

Note

The chosen event cannot be a sibling of the edited one (another child of the same gate): the change is rejected with the message This ID already exists as a child of this parent. Undeveloped Events and gates do not offer the list, since their ID cannot be the ID of another node of the project.

See Computation for more information about the parameters of the primary events.

• Change to Basic/Undeveloped Event

By clicking Change to Basic Event or Change to Undeveloped Event, the node will change from Basic to Undeveloped event or viceversa.

Fast node creation

Building a fault tree node by node through the Add child form is slow when the structure is already known and only the topology has to be captured. To speed this up, Robin provides the Add fast child actions, which create a node in a single click, without opening any form.

A node created this way gets an automatic ID code, formed by a prefix that depends on the type of node (AND, OR, VOTE, BE, UE, TF or R) followed by an incremental number, and the default description TBD. Both can be edited afterwards through Change information or Change parameters.

The fast child actions are available in two places:

• In the panel that opens when clicking on a gate, under the label Add fast child, with one button per type of node: + AND, + OR, + BE, + UE, + TG, + R and + VG. Next to the label, a quantity selector allows the creation of several identical children at once, which is useful for redundant configurations where the same structure is repeated.

• In the right-click context menu, under the Add Fast Child submenu.

Note

The quantity selector allows adding from ×1 up to ×5 children per click.

Note

When the node created is a Vote gate, Robin asks for the value of K before creating it. See the Computation section for details.

Keyboard shortcuts

The fast child actions have a keyboard shortcut each. Select a gate in the diagram and press the corresponding combination to add a child of that type below it:

Action	Shortcut
Add AND gate	CTRL+A
Add OR gate	CTRL+O
Add Basic Event	CTRL+B
Add Undeveloped Event	CTRL+U
Add Transfer gate	CTRL+G
Add Remark node	CTRL+Q

These shortcuts are added to the ones already available in the diagram:

Action	Shortcut
Copy	CTRL+C
Cut	CTRL+X
Paste	CTRL+V
Undo	CTRL+Z
Redo	CTRL+Y
Move node left/right	CTRL+Left/Right
Maximize the diagram	CTRL+M

Note

The Vote gate has no keyboard shortcut, since it always requires the value of K to be introduced before the node can be created.

Note

The shortcuts only act when the focus is inside the diagram. They are disabled while the user is typing in a form or working outside the diagram area.

Checking the Fault Tree

Before computing the probability or exporting a report, Robin can verify the consistency of the loaded fault tree. The check reports two levels of issues:

• Warnings: Errors that prevent the failure rate from being computed. They are:

  • An AND or an OR gate without any child

  • A Vote gate with less than 2 children

  • A Vote gate whose threshold is not lower than its number of children (\(K \geq N\))

• Cautions: Recommendations to apply before computing, which do not block the calculation. They are:

  • A branch switched off, since it is left out of the failure rate. It is reported once, on the node where the branch starts, and not on each node below it

  • A node left with the default description TBD

  • A node left with the automatically generated ID code (e.g. AND-12 or ID-TOP-GATE-3)

Note

The nodes of a switched-off branch are not checked, since they are not part of the computation: apart from the caution of the branch itself, they report no warnings or cautions. A switched-off Remark is not reported, since Remarks never take part in the computation.

Note

Cautions typically appear on nodes created with the fast child actions described above, which are exactly the nodes still pending to be named and described.

Cautions do not block any action, but they are not left unnoticed: when the loaded fault tree has any, the windows to calculate the probability or the cut sets, to print and to export show a yellow banner at the top with the number of cautions (e.g. The FT TOP-1 has 2 cautions). The Check the FT button of the toolbar lists them.

Two options are available at system level, in the FT Check Settings of the FTA settings, to adapt the check to the way the system is built. They apply only to the selected system:

• Allow calculate/print/export with warnings: When active, the probability and the cut sets can be calculated and the report can be printed or exported even if the check reports warnings. It is disabled by default.

• Remark gates count as children: Remark gates do not take part in the computation, so by default they do not count when verifying that a gate has at least one child. Activating this option makes them count.

Checking the Project

A gate can be used in several places of the project: repeated in a fault tree, added to other fault trees with its branch, shown as a Transfer Gate inside another fault tree, or in other systems. Each place holds a copy of the gate with the same ID, and calculating a fault tree gives its probability to every copy of its gates, so all the copies must be the same gate.

The Check the Project button, next to Check the FT in the toolbar of the diagram, compares the copies of every gate repeated in the project, in all its systems, and lists the gates whose copies are not the same. Two copies are different when:

• They are not the same type of gate. A Transfer Gate counts as the gate it folds.

• They are Vote gates with a different threshold (\(K\)).

• Their children are not the same, or one of them has no children.

• A node below the gate is switched off in one copy only.

• There is a difference further down the branch.

The result opens in a panel on the right of the diagram, where the Event/Gate information opens, and the diagram stays in use on its left. The button is highlighted while the panel is open, and clicking it again checks the project again (after changing the fault trees, for instance). Esc closes it.

The top of the panel shows how many repeated gates were checked and how many have copies that differ, and how the children of a version are marked, and stays in sight while the cards scroll below it. Each of those gates is a card: its header shows the ID, the description, the number of copies and the number of versions, and clicking it folds or unfolds the card. The double arrow at the right of the title of the panel unfolds every card at once while one of them is folded (Expand all), and folds them all when all of them are unfolded (Collapse all). The information icon next to the title of the panel explains, on hover, what is compared. When more than five gates are listed, the cards open folded, so that the whole list can be read at a glance.

As in the list of the search and in the one of the ID of a new child, the gates, their copies and their children show on their left the colour of their type in the diagram: AND gate, OR or Vote gate, Transfer gate or primary event. A copy shown as a Transfer Gate has the colour of the gate it folds.

Inside a card there is a block for each version of the gate:

• Version: The first version, marked as Reference, is the copy that is the top event of its fault tree or, when there is none, the version with most copies. The rest are compared with it.

• Copies: The fault tree of each copy of that version, with its system and its parent, or the Top event label. A long list shows the first five copies: Show all ... copies unfolds the rest and Show fewer folds them again.

• Below the gate: The children of the gate. Against the first version, a highlighted child is not in it (or is switched off differently), a crossed-out one is only in the first version, and a grey one with the power icon is switched off.

• Differences with version 1: What makes this version different from the first one.

Note

A difference further down is reported on every gate above it as well: fixing the gate whose children differ fixes the gates above.

Note

Only the gates that belong to a fault tree are compared: the unused gates are left out, as well as the Remarks, which do not take part in the computation. The order of the children does not matter.

Showing a copy in the diagram

Clicking on a copy shows its fault tree in the diagram without reloading the page: the diagram moves to the copy and highlights it, and the copy turns black in the panel while its fault tree is the one on screen. Clicking on the copies one after the other compares them in the diagram. While the fault tree loads only the diagram waits, blurred under the loading icon: the System and Top Event dropdowns and the title already show the system and the fault tree of the copy, and the rest of the page can still be used.

• When the copy is in another system of the project, the page changes to that system, as if it had been chosen in the System dropdown: the System and Top Event dropdowns, the title and the fault trees of the calculate and print windows are the ones of that system.

• When the copy is inside a Transfer Gate, the diagram goes inside it, as Go inside the Transfer Gate does, and the Top Event dropdown shows the Fault Tree of the Transfer Gate.

• Selecting a node of the diagram shows its Event/Gate information in the place of the panel. Esc closes it and brings the panel back as it was; Esc again closes the panel.

• Ctrl + click on a copy opens it in another tab of the browser.

Note

While a calculation is running, the copies of another system cannot be shown until it ends: the calculation sends its fault trees to the system it started in.

Making the copies the same

Users who can change the fault trees see a Use this one button under the number of each version. It gives the branch of that version to every copy of the gate that is not like it, in all the fault trees and systems of the project.

Robin first shows, in the card of the gate, what would change in each copy, without changing anything yet: how many nodes would be removed, added or changed. It also warns when comments of the nodes removed would be deleted, or when MSG-3 tasks would lose the link to a CMR node removed. Click on Replace to make the change, or on Cancel to leave everything as it is.

Each copy keeps its place in its fault tree (its parent, its fault tree and its system) and takes the type of gate, the vote threshold and the branch of the version picked, with the same nodes switched off:

• The children it shares with the version picked stay, and are made the same in turn.

• The children the version picked does not have are deleted, with their branch and their comments.

• The children it lacks are copied from the version picked, with their branch and their comments.

• Its Remarks stay as they are.

• A copy shown as a Transfer Gate stays shown as one.

After the change, a message at the top of the panel lists the fault trees changed and the check runs again, with the cards unfolded as they were. The probabilities of those fault trees are out of date, so the calculator turns red until they are calculated again. Undo, in each of them, goes back to how it was before the change. If the fault tree on screen changed, it is drawn again at once.

Note

A copy is left out, with the reason, when the version picked has, below the gate, one of the nodes above the copy: its fault tree would contain itself.