Snippets (text quotes and extracts from authoritative sources)

A Snippet is a short quote or extract (typically a phrase, a sentence, or at most a few sentences) from an authoritative source document such as a specification, technical manual, or design manual. Throughout this site, content is often related to supporting Snippets and each Snippet page links back to the content pages that reference it! The Snippet and Note concepts are very closely related and they support each other.

The Snippet concept is also at the heart of the Parsing Analysis recipe for UML® and SysML®

Kind Snippet quote/extract Source UML keywords SysML keywords Keywords
INFO Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin. Wikipedia
INFO Due to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas. Wikipedia
INFO Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Wikipedia
INFO A quark is a type of elementary particle and a fundamental constituent of matter. Wikipedia
INFO The resulting attraction between different quarks causes the formation of composite particles known as hadrons Wikipedia
INFO Unlike leptons, quarks possess color charge, which causes them to engage in the strong interaction. Wikipedia
INFO Both of these decays imply that color is no longer a property of the byproducts. Wikipedia
INFO Uncharged mesons may decay to photons. Wikipedia
INFO Charged mesons decay (sometimes through mediating particles) to form electrons and neutrinos. Wikipedia
INFO All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Wikipedia
INFO In particle physics, mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by strong interactions. Wikipedia
INFO Four closely related Δ baryons exist: Δ++ (constituent quarks: uuu), Δ+ (uud), Δ0 (udd), and Δ− (ddd), which respectively carry an electric charge of +2 e, +1 e, 0 e, and −1 e. Wikipedia
INFO The Δ baryons have ... a spin of ​3⁄2 ... Wikipedia
INFO In particle physics, a hadron ... is a subatomic composite particle made of two or more quarks ... Wikipedia
INFO Exotic baryons containing five quarks (known as pentaquarks) have also been discovered and studied. Wikipedia
INFO Since baryons are made of three quarks [DISPUTED], their spin vectors can add to make a vector of length S = 3/2, which has four spin projections (Sz = +3/2, Sz = +1/2, Sz = −1/2, and Sz = −3/2), or a vector of length S = 1/2 with two spin projections ... Wikipedia
INFO If two quarks have unaligned spins, the spin vectors add up to make a vector of length S = 0 and has only one spin projection (Sz = 0), etc. Wikipedia
INFO Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length S = 1 and three spin projections (Sz = +1, Sz = 0, and Sz = −1). Wikipedia
INFO Because spin projections vary in increments of 1 (that is 1 ħ), a single quark has a spin vector of length 1/2, and has two spin projections (Sz = +1/2 and Sz = −1/2). Wikipedia
INFO Quarks are fermionic particles of spin 1/2 (S = 1/2). Wikipedia
INFO Protons are spin-1/2 fermions and are composed of three valence quarks, making them baryons (a sub-type of hadrons). Wikipedia
INFO The neutron ... is a spin-½ fermion. Wikipedia
INFO The most familiar baryons are protons and neutrons, both of which contain three quarks, and for this reason these particles are sometimes described as triquarks. Wikipedia
INFO They are also classified as fermions, i.e., they have half-integer spin. Wikipedia
INFO Baryons belong to the hadron family of particles, which are the quark-based particles. Wikipedia
INFO In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Wikipedia
INFO According to the spin-statistics theorem in any reasonable relativistic quantum field theory, particles with integer spin are bosons, while particles with half-integer spin are fermions. Wikipedia
INFO Some fermions are elementary particles, such as the electrons, and some are composite particles, such as the protons. Wikipedia
INFO Fermions differ from bosons, which obey Bose–Einstein statistics. Wikipedia
INFO Fermions include all quarks and leptons, as well as all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei. Wikipedia
INFO In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin 1/2, 3/2 etc. These particles obey the Pauli exclusion principle. Wikipedia
INFO The Pauli exclusion principle is the quantum mechanical principle which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously. Wikipedia
INFO sz is the spin projection quantum number along the z-axis. Wikipedia
INFO there are only two possible values for a spin-1/2 particle: sz = +1/2 and sz = -1/2. These correspond to quantum states in which the spin component is pointing in the +z or −z directions respectively, and are often referred to as "spin up" and "spin down" Wikipedia
INFO Furthermore, it means that a lepton can have only two possible spin states, namely up or down. Wikipedia
INFO Leptons are spin 1/2 particles. The spin-statistics theorem thus implies that they are fermions and thus that they are subject to the Pauli exclusion principle: No two leptons of the same species can be in the same state at the same time. Wikipedia
INFO The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge. Wikipedia
INFO As the symbol e is used for the elementary charge, the electron is commonly symbolized by e−, where the minus sign indicates the negative charge. Wikipedia
INFO Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. Wikipedia
INFO Electrons have an electric charge of −1.602176634×10−19 coulombs, which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge. Wikipedia
INFO The invariant mass of an electron is approximately 9.109×10−31 kilograms, or 5.489×10−4 atomic mass units. On the basis of Einstein's principle of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV. Wikipedia
INFO In theory, a particle and its anti-particle (for example, a proton and an antiproton) have the same mass, but opposite electric charge and other differences in quantum numbers. For example, a proton has positive charge while an antiproton has negative ... Wikipedia
INFO In modern physics, antimatter is defined as matter which is composed of the antiparticles (or "partners") of the corresponding particles of 'ordinary' matter. Wikipedia
INFO While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. The opposite is also true: the antiparticle of the positron is the electron. Wikipedia
INFO For example, the antiparticle of the electron is the antielectron (which is often referred to as positron). Wikipedia
INFO In particle physics, every type of particle is associated with [an] antiparticle with the same mass but with opposite physical charges (such as electric charge). Wikipedia
INFO According to certain theories, neutrinos may be their own antiparticle. It is not currently known whether this is the case. Wikipedia
INFO For every lepton flavor, there is a corresponding type of antiparticle, known as an antilepton, that differs from the lepton only in that some of its properties have equal magnitude but opposite sign. Wikipedia
INFO electromagnetism ... is proportional to charge, and is thus zero for the electrically neutral neutrinos. Wikipedia
INFO Unlike quarks, however, leptons are not subject to the strong interaction, but they are subject to the other three fundamental interactions: gravitation, the weak interaction, and to electromagnetism ... Wikipedia
INFO Leptons have various intrinsic properties, including electric charge, spin, and mass. Wikipedia
INFO a helium atom in the ground state has spin 0 and behaves like a boson, even though the quarks and electrons which make it up are all fermions. Wikipedia
INFO In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei. Wikipedia
INFO The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states. Wikipedia
INFO Thus electrons are stable and the most common charged lepton in the universe, whereas muons and taus can only be produced in high energy collisions (such as those involving cosmic rays and those carried out in particle accelerators). Wikipedia
INFO The heavier muons and taus will rapidly change into electrons and neutrinos through a process of particle decay: the transformation from a higher mass state to a lower mass state. Wikipedia
INFO Electrons have the least mass of all the charged leptons. Wikipedia
INFO and the third are the tauonic leptons, comprising the tau ( τ− ) and the tau neutrino ( ν τ) Wikipedia
INFO the second are the muonic leptons, comprising the muon ( μ− ) and the muon neutrino ( ν μ); Wikipedia
INFO The first-generation leptons, also called electronic leptons, comprise the electron ( e− ) and the electron neutrino ( ν e); Wikipedia
INFO There are six types of leptons, known as flavours, grouped in three generations. Wikipedia
INFO The best known of all leptons is the electron. Wikipedia
INFO Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. Wikipedia
INFO Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. Wikipedia
INFO Two main classes of leptons exist, charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos). Wikipedia
INFO In particle physics, a lepton is an elementary particle of half-integer spin (spin ​1⁄2) that does not undergo strong interactions. Wikipedia
INFO «effbd» Specifies that the activity conforms to the constraints necessary for EFFBD. OMG Systems Modeling Language (SysML) 1.6 Activity «effbd» non-normative
INFO «nonStreaming» Used for activities that accept inputs only when they start, and provide outputs only when they finish. The activity has no streaming parameters. OMG Systems Modeling Language (SysML) 1.6 Activity «nonStreaming» non-normative
INFO «streaming» Used for activities that can accept inputs or provide outputs after they start and before they finish. The activity has at least one streaming parameter. OMG Systems Modeling Language (SysML) 1.6 Activity «streaming» non-normative
INFO The stereotype does not override UML token offering semantics, just indicates what happens to the token when it is accepted. When the stereotype is not applied, the semantics is as in UML, specifically, tokens arriving at object nodes do not replace ... OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token Overwrite, «overwrite»
INFO For object nodes that are the target of continuous flows, «overwrite» and «nobuffer» have the same effect. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token Overwrite, «overwrite», Continuous, «continuous», NoBuffer, «noBuffer»
INFO The number of tokens replaced is equal to the weight of the incoming edge, which defaults to 1. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token Overwrite, «overwrite»
INFO A null token removes all the tokens already there. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token, null token, null Overwrite, «overwrite»
INFO Tokens arriving at a full object node with the Overwrite stereotype applied take up their positions in the ordering as normal, if any. The arriving tokens do not take the positions of the removed tokens. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token Overwrite, «overwrite»
INFO For upper bounds greater than one, the token removed is the one that has been in the object node the longest. For FIFO ordering, this is the token that is next to be selected, for LIFO it is the token that would be last to be selected. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token, ObjectNodeOrderingKind::FIFO, ObjectNodeOrderingKind::LIFO, ObjectNodeOrderingKind Overwrite, «overwrite»
INFO This is typically used on an input pin with an upper bound of 1 to ensure that stale data is overridden at an input pin. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper, InputPin, Action::/input, token Overwrite, «overwrite»
INFO When the «overwrite» stereotype is applied to object nodes, a token arriving at a full object node removes one that is already there before being added (a full object node has as many tokens as allowed by its upper bound). OMG Systems Modeling Language (SysML) 1.6 ObjectNode, MultiplicityElement::/upper Overwrite, «overwrite»
INFO NoBuffer::1_not_overwrite The «nobuffer» and «overwrite» stereotypes cannot be applied to the same element at the same time OMG Systems Modeling Language (SysML) 1.6 ObjectNode, ActivityNode::outgoing, InputPin, Action::/input «noBuffer», NoBuffer, Overwrite, «overwrite»
INFO The stereotype does not override UML token offering semantics; it just indicates what happens to the token when it is accepted. When the stereotype is not applied, the semantics are as in UML, specifically, tokens arriving at an object node ... OMG Systems Modeling Language (SysML) 1.6 ObjectNode, ActivityNode::outgoing, InputPin, Action::/input «noBuffer», NoBuffer
INFO For object nodes that are the target of continuous flows, «nobuffer» and «overwrite» have the same effect. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, ActivityNode::outgoing, InputPin, Action::/input «noBuffer», NoBuffer, Continuous, «continuous», «overwrite», Overwrite
INFO This is typically used with fast or continuously flowing data values, to prevent buffer overrun, or to model transient values, such as electrical signals. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, ActivityNode::outgoing, InputPin, Action::/input «noBuffer», NoBuffer
INFO When the «nobuffer» stereotype is applied to object nodes, tokens arriving at the node are discarded if they are refused by outgoing edges, or refused by actions for object nodes that are input pins. OMG Systems Modeling Language (SysML) 1.6 ObjectNode, ActivityNode::outgoing, InputPin, Action::/input «noBuffer», NoBuffer
INFO Discrete rate is a special case of rate of flow ... where the increment of time between items is a non-zero. Examples include the production of assemblies in a factory and signals set at periodic time intervals. OMG Systems Modeling Language (SysML) 1.6 Discrete, «discrete», Rate, Rate::rate
CONSTRAINT, INFO When the «probability» stereotype is applied to output parameter sets, it gives the probability the parameter set will be given values at runtime. These shall be between zero and one inclusive, and add up to one for output parameter sets of the same ... OMG Systems Modeling Language (SysML) 1.6 Parameter::parameterSet, ParameterSet «probability», Probability, Probability::probability
CONSTRAINT, INFO When the «probability» stereotype is applied to edges coming out of decision nodes and object nodes, it provides an expression for the probability that the edge will be traversed. These shall be between zero and one inclusive, and add up to one ... OMG Systems Modeling Language (SysML) 1.6 DecisionNode, ObjectNode, ActivityEdge «probability», Probability, Probability::probability
CONSTRAINT 1_lower_is_0 A parameter with the «optional» stereotypes applied shall have multiplicity.lower equal to zero, otherwise multiplicity.lower shall be greater than zero OMG Systems Modeling Language (SysML) 1.6 Parameter, MultiplicityElement::/lower, multiplicity «optional», Optional, required
INFO When the «optional» stereotype is applied to parameters, the lower multiplicity shall be equal to zero. This means the parameter is not required to have a value for the activity or any behavior to begin or end execution ... OMG Systems Modeling Language (SysML) 1.6 Parameter, MultiplicityElement::/lower, multiplicity «optional», Optional, Optional, required
INFO Once the test fails and the loop is completed, the tokens on the bodyOutput OutputPins from the last iteration are moved to the result OutputPins and offered on any edges outgoing from those OutputPins. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::loopVariable, OutputPin, LoopNode::bodyOutput
INFO After the completion of each execution of the bodyPart of the LoopNode, any remaining tokens on the loopVariable OutputPins are destroyed and tokens on the bodyOutput OutputPins are copied to the corresponding loopVariable OutputPins so that they are ... Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::loopVariable, OutputPin, LoopNode::bodyOutput
INFO When the LoopNode begins executing, the tokens on the loopVariableInput InputPins are moved to the corresponding loopVariable OutputPins before the first iteration of the loop. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::loopVariable, ActivityNode::outgoing, ActivityEdge, OutputPin, LoopNode::loopVariableInput, InputPin
INFO If a LoopNode has loopVariable OutputPins, then it must also have matching sets of loopVariableInput InputPins, bodyOutput OutputPins (owned by Actions within the bodyPart), and result OutputPins. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::loopVariable, OutputPin, LoopNode::loopVariableInput, LoopNode::bodyOutput, LoopNode::result, InputPin
INFO A LoopNode may also define a set of loopVariable OutputPins used to hold intermediate values during each loop iteration. These OutputPins may have outgoing ActivityEdges, in order to make the values they hold available within the test and bodyPart ... Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::test, LoopNode::loopVariable, ActivityNode::outgoing, ActivityEdge, OutputPin
INFO After each execution of the bodyPart, the test section is executed again, for the next iteration of the loop. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::test, LoopNode::bodyPart, LoopNode:decider
INFO The test section has an Action owning the decider OutputPin with type Boolean identified by the LoopNode. When the test section has completed execution, if the value on the decider OutputPin is true, then the bodyPart is executed. Otherwise ... Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::test, LoopNode::bodyPart, LoopNode:decider
INFO Execution of the test section may precede or follow execution of the bodyPart, depending on whether isTestFirst is true or false, respectively. ... If the bodyPart is executed first (isTestFirst=false), it is always executed at least once ... Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::test, LoopNode::bodyPart, LoopNode::isTestedFirst
INFO The setupPart of a LoopNode is executed first. When the setupPart has completed execution, the iterative execution of the loop begins. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::setupPart
INFO Any ExecutableNode in the LoopNode must be included in the setupPart, test or bodyPart for the LoopNode. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::setupPart, LoopNode::test, LoopNode::bodyPart, ExecutableNode
INFO A LoopNode is a StructuredActivityNode that represents an iterative loop. A LoopNode consists of a setupPart, a test and a bodyPart, which identify subsets of the ExecutableNodes contained in the LoopNode. Unified Modeling Language 2.5.1 Activity, Activity Diagram, LoopNode, LoopNode::setupPart, LoopNode::test, LoopNode::bodyPart, ExecutableNode
INFO This means that an Activity model in which non-determinacy occurs may be subject to timing issues and race conditions. It is the responsibility of the modeler to avoid such conditions in the construction of the Activity model, if they are not desired. Unified Modeling Language 2.5.1 ActivityEdge, ActivityNode::outgoing, ActivityNode, token
INFO If a token is offered to multiple ActivityNodes at the same time, it shall be accepted by at most one of them, but exactly which one is not completely determined by the Activity flow semantics. Unified Modeling Language 2.5.1 ActivityEdge, ActivityNode::outgoing, ActivityNode, token