=Paper= {{Paper |id=Vol-3007/2021-paper-2 |storemode=property |title=A Concept for Self-Explanation of Macro-Level Behaviourin Lifelike Computing Systems |pdfUrl=https://ceur-ws.org/Vol-3007/2021-paper-2.pdf |volume=Vol-3007 |authors=Martin Goller,Sven Tomforde |dblpUrl=https://dblp.org/rec/conf/lifelike/GollerT21 }} ==A Concept for Self-Explanation of Macro-Level Behaviourin Lifelike Computing Systems== https://ceur-ws.org/Vol-3007/2021-paper-2.pdf
                     A Concept for Self-Explanation of Macro-Level Behaviour
                                  in Lifelike Computing Systems
                                                    Martin Goller1 and Sven Tomforde1
                                 1
                                     Intelligent Systems, Christian-Albrechts-Universität zu Kiel, Germany
                                               goller.cau@gmail.com / st@informatik.uni-kiel.de


                              Abstract                                                 takes up and continues the original motivation of the OC
                                                                                       and AC initiatives.
  The basic idea of developing future ’lifelike’ systems is to                            In this article, we note that in addition to the obvious
  transfer qualities in technical utilisation that go beyond well-
  established mechanisms such as self-adaptation, learning,                            lifelike properties such as evolution and continuous adap-
  and robustness. In this paper, we argue that the resulting sys-                      tation to the ’living space’ or ’environmental niche’ as well
  tems will need components to self-explain their behaviour - if                       as focused response mechanisms (to name only the obvious
  we want to avoid acceptance issues that result from surpris-                         examples), another prominent challenge comes to the fore
  ing and irritating system behaviour. Such self-explaining be-                        in the acceptance of such systems by the human users (or
  haviour needs to answer the questions of when, what and how
  explanations should be provided to the user. We review exist-                        better: stakeholders or influenced persons). This raises the
  ing metrics, outline a concept of how to address the ’when’                          question of how such systems can explain their behaviour to
  question and identify corresponding research challenges to-                          humans in an automated way, which in turn leads directly
  wards an automated generation of explanations.                                       to the two crucial questions: When are explanations of be-
                                                                                       haviour necessary? And: What needs to be explained.
                                                                                          From a developer’s point of view, this primarily means
                       I. Introduction
                                                                                       that we need a concept to answers the question of ’when’,
Recent trends in information and communication technol-                                which then enables us to answer the ’what’. Therefore,
ogy entailed increasingly autonomous systems that adapt                                this article explains a concept to measure system behaviour,
their own behaviour and try to optimise it over time – result-                         whereupon abnormal behaviour of these measurements will
ing in so-called self-adaptive and self-organising (SASO)                              then serve as an answer to the question ’when’.
systems. Initiatives such as Organic (Müller-Schloer and                                 Building on recent work, we present a measurement
Tomforde (2017)) and Autonomic Computing (Kephart and                                  framework for system behaviour that forms the basis for
Chess (2003)) are concrete manifestations and pioneers of                              such an explanation framework (Section II). In addition,
this trend, which is supported by new applications such as                             we discuss possible further variables that can be relevant
autonomous driving (Levinson et al. (2011)) or the Internet                            for lifelike behaviour and can therefore be integrated into
of Things (Weber and Weber (2010)). SASO technology                                    the framework. On this basis, we discuss a concept to
is understood as an approach to keeping the complexity of                              automatically detect events that serve as triggers for self-
increasingly integrated, open and dynamic systems manage-                              explanations, which is combined with a principled, possible
able, as it is no longer possible to plan all possibilities in                         use to answer the question ’what’ (Section III). Since this
advance at design time. At the same time, the integration of                           is intended as a first concept, we highlight the most urgent
machine learning methods is intended to create novel possi-                            research challenges to automatically generate the resulting
bilities to react appropriately to the unknown and at the same                         self-explanations. The article concludes with a summary and
time continuously strive for better behaviour.                                         an outlook on how the defined concepts can be explored and
   Even though SASO technology already had its roots                                   implemented.
in cybernetics and has been drastically strengthened again
in the last two decades (perhaps starting from Tennen-
                                                                                                 II. A Measurement Framework for
house’s Proactive Computing, see (Tennenhouse (2000)),
and Weiser’s vision of Pervasive Computing, see (Weiser                                          Macro-Level Behaviour Assessment
(1999))), we can state that controllability and reacting or                            The basis of our approach to self-explanatory mechanisms
adapting to the unknown remain the central challenges. This                            of lifelike technical systems is the possibility of quantifying
realisation leads, among other things, to the approach of                              system behaviour by means of (external) observation. To
making technical systems even more lifelike, which e.g.                                this end, in this section, we first present our system model,




                Copyright ©2021 for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
which we currently assume - and which can form the ba-
sis for future lifelike systems. Using this system model, we
then explain existing and potential approaches for quantify-
ing system properties.

System Model
In this article, we refer to a technical system S as a collection
A of autonomous subsystems ai that are able to adapt their
behaviour based on self-awareness of the internal and ex-
ternal conditions. We further assume that such a subsystem
is an entity that interacts with other entities, i.e., other sys-
tems, including hardware, software, humans, and the phys-           Figure 1: Schematic illustration of a subsystem ai
ical world with its natural phenomena. These other entities         from (Tomforde et al. (2011)). The arrows from the sen-
are referred to as the environment of the given system. The         sors and PS to the CM indicate observation flows, while the
system boundary is the common frontier between the system           arrows from the CM to the PS and the actuators indicate con-
and its environment.                                                trol flows. Dashed arrows emphasise a possible path that is
   Each ai ∈ A is equipped with sensors and actuators (both,        typically not used. Not shown: The CM is able to communi-
physical or virtual). Internally, each ai consists of two parts:    cate with other CMs in the shared environment to exchange
The productive system part PS, which is responsible for the         information such as sensor reading and to negotiate policies
basic purpose of the system, and the control mechanism CM,          using the communication bus.
which controls the behaviour of the PS (i.e., performs self-
adaptation) and decides about relations to other subsystems.
In comparison to other system models, this corresponds to           system, and are the result of the self-adaptation process of
the separation of concerns between System under Observa-            the CM .
tion and Control (SuOC) and Observer/Controller tandem                 This system model describes an approach based on the
(Tomforde et al. (2011)) in the terminology of Organic Com-         current state-of-the-art in the field of self-adaptive and self-
puting (OC) (Tomforde et al. (2017b)) or Managed Resource           organising systems. We assume that ongoing research to-
and Autonomic Manager in terms of Autonomic Comput-                 wards more lifelike systems will shift the boundaries in
ing (Kephart and Chess (2003)). Figure 1 illustrates this con-      terms of the underlying technology as well as the possibility
cept with its input and output relations. The user describes        to alter higher-levelled design decisions – but it will most
the system purpose by providing a utility or goal function U        likely not result in entirely new design concepts. In turn, we
which determines the behaviour of the subsystem. The User           assume that fundamental questions will arise about how the
usually takes no further action to influence the decisions of       CM evolves according to the characteristics of its ’environ-
the subsystem. Actual decisions are taken by the productive         mental niche’, for instance, but the separation of concerns
system and the CM based on the external and internal con-           between CM and PS remain visible.
ditions and messages exchanged with other subsystems. We
model each subsystem to act autonomously, i.e., there are           Standard Measures
no control hierarchies in the overall system. Please note that      Traditionally, the success and the behaviour of a technical
for the context of this article an explicit local configuration     system is quantified using the primary purpose of the appli-
of the PS is necessary – which in turn limits the scope of          cation. In the first place, this directly refers to the system
the applicability of the proposed method. Furthermore, each         goal. Based on the categorisation proposed by McGeoch in
subsystem must provide read-access to the configuration.            McGeoch (2012), we distinguish between the two perfor-
   At each point in time, the productive system of each ai is       mance aspects quality of the solution and time required for
configured using a vector ci . This vector contains a specific      the solution. The latter defines how much time the system
value for each control variable that can be altered to steer the    required to solve the given purpose or application – where
behaviour, independently of the particular realisation of the       the time can be given in CPU cycles, in real-time, or even in
parameter (e.g., as real value, boolean/flag, integer or cate-      a logical time. Intuitively, such a time-based measure comes
gorical variable). Each subsystem has its own configuration         with high precision depending on the underlying resolution
space, i.e. an n-dimensional space defining all possible real-      but it does not include any statements about the quality or
isations of the configuration vector. The combination of the        generality. In particular, it may depend on the specific hard-
current configuration vectors of all contained subsystems of        ware equipment that has been used in the experiments. In
the overall system S defines the joint configuration of S.          turn, the quality itself (which may be expressed in a degree
We assume that modifications of the configuration vectors           of goal achievement) says nothing about the time required
are done by the different CM only, i.e. locally at each sub-        to accomplish the goal.
   These overarching aspects of system behaviour are aug-          De Wolf and Holvoet (2004).
mented with a more theoretical analysis of the applicabil-             c) Self-adaptation refers to the ability of systems to
ity. In particular, given techniques such as the O(n) nota-        change their behaviour according to environmental condi-
tion, runtime and memory complexity are quantified. This           tions, typically with the goal to increase a utility func-
can be extended with verification of processes, i.e., guaran-      tion. The degree of adaptivity can be measured using static
tees that may be quantified in terms of coverage or degree         (Schmeck et al. (2010)) and dynamic (Tomforde and Goller
of guarantee-able behaviour. As an alternative, the ’restore-      (2020)) approaches.
invariant approach’ by Nafz et al. Nafz et al. (2011) estab-           d) Scalability is a property that defines how far the under-
lishes a formal framework for self-organisation behaviour          lying mechanisms are still promising if the number of partic-
that may serve as a quantifiable basis.                            ipants grows strongly. Quantitatively, this can be expressed
   In addition to these considerations, the robustness and re-     as an exponent for the control overhead, for instance.
silience of systems, as well as their behaviour, can be quanti-        e) Stability is to a certain degree a meta-measure applied,
fied using specific metrics. One recent example from the do-       e.g., to the degrees of self-adaptation and self-organisation.
main of Organic Computing systems can be found in (Tom-            It determines how far the metrics are static allowing for stan-
forde et al. (2018)).                                              dard changes and identifying deviations from the expected
                                                                   behaviour. An example can be found in (Goller and Tom-
Self-Adaptation-based Measures                                     forde (2020)).
Due to the shift in responsibility as visualised by our system         f) Variability or Heterogeneity are terms referring to pop-
model depicted in Figure 1 – a CM is added to the PS that          ulation of individual subsystems as they focus on the dif-
performs (semi-)autonomous decisions – research on SASO            ferences in the behaviour, the capabilities or the strategies
systems entailed augmenting the measurement framework              followed by the subsystems. Examples can be found in
by several SASO-specific metrics. For instance, Kaddoum et         (Schmeck et al. (2010)) and (Lewis et al. (2015)).
al. (Kaddoum et al. (2010)) discuss the need to refine classi-         g) Mutual influences among distributed autonomous sub-
cal performance metrics to SASO purposes and present spe-          systems indicate that the decisions of one have an impact
cific metrics for self-adaptive systems. They distinguish be-      (e.g., on the degree of utility achievement) of another sub-
tween “nominal” and “self-*” situations and their relations:       system (Rudolph et al. (2019)). An example for a quan-
The approach measures the operation time about the adapta-         tification technique based on the utilisation of dependency
tion time to determine the effort. This includes aspects such      measures is given inRudolph et al. (2016).
as the adaptation speed to detected changes. Some of the
developed metrics have been investigated in detail by Ca-          Possible Lifelike-oriented Measures
mara et al. for software architecture scenarios (Cámara et al.    Considering the concept of lifelike technical systems and
(2014)). Besides, success and adaptation efforts and ways to       their desired capabilities, the set of existing metrics is prob-
measure autonomy have been investigated, see e.g. (Gronau          ably not sufficient enough to cover the entire behaviour. In
(2016)).                                                           particular, we will have to investigate novel measurement
    In addition to these goal- and effort-based metrics, several   techniques that explicitly cover lifelike attributes. Although
further measurements indicate a macro-level behaviour of a         there is currently no exact definition of what lifelike com-
set of autonomous subsystems. The most important are:              puting systems are, we can approach the question of what
    a) Emergence is basically described as the emergence           is missing in the measurement framework by considering
of macroscopic behaviour from microscopic interactions of          ’qualities of life’ that we aim to transfer to technical usage
self-organised entities (Holland (2000)). In the context of        and that go beyond the SASO-based scalability, adaptation,
SASO systems, this refers to the formation of patterns in the      organisation, or robustness questions. In particular, we iden-
system-wide behaviour, for instance. Examples for quantifi-        tified the following aspects as primary options based on the
cation methods are (Mnif and Müller-Schloer (2011)) and           considerations of how we consider lifelike systems outlined
(Fernández et al. (2014)).                                        in Section I:
    b) Self-organisation can be expressed as a degree to               First, lifelike system will evolve over time which may in-
which the autonomous subsystems forming an overall SASO            clude an adaptation of its primary usage. Consequently, a
system decide about the system’s structure without ex-             first measure should aim at quantifying the evolution be-
ternal control, where the structure is expressed as in-            haviour itself and a second one the coverage of the primary
teraction/cooperation/relation among individual subsystems         purpose. The latter case continues the ideas formulated in
(Müller-Schloer and Tomforde (2017)). Examples of quan-           the Organic Computing initiative when defining the property
tification methods are using a static approach (see (Schmeck       of ’flexibility’, i.e. how far a SASO system can react appro-
et al. (2010)) and methods using a dynamic approach, see           priately to changing goal functions (Becker et al. (2012)).
(Tomforde et al. (2017a)). An alternative discussion of                Second, this evolution corresponds to an adaptation to the
self-organisation and its relation to emergence is given by        niche in which the system survives. This may be expressed
with a measure of ’fitness in the niche’ or ’degree of niche       (2020) (based on a multi-level reasoning approach using
appropriateness’.                                                  temporal models).
   Third, such an evolution implies that the system is some-          In contrast to these approaches, we propose to develop
how converted (or better: converts itself). Besides the de-        a self-explanation component for lifelike technical systems
scription of this process of time, a more static measure based     that builds upon the metrics outlined above and establishes
on the design can aim at determining a ’degree of converta-        an observation and explanation loop. The idea of such a self-
bility’, i.e. the freedom to which the system can evolve dur-      explanation is that this should cover the following aspects:
ing operation.
                                                                    • It should only be provided if the system recognises unan-
   Fourth, this may include a transfer to an entirely different
                                                                      ticipated behaviour or abrupt shifts that are perceived by
niche, or in other words to another problem domain. This
                                                                      humans that interact with the system (otherwise we face
can be expressed in a static manner by comparing the current
                                                                      an attention problem of users)
problem space with the initial one or in a dynamic manner
by a degree of transfer that the system has undergone.              • The explanations should contain information about what
   Fifth, such a lifelike, evolutionary behaviour is done in          changed and why this change happens, which includes the
the context of the environmental conditions, which includes           triggers that have been identified as root causes (e.g. a
the presence of other subsystems in open system constella-            failure of a component, abnormal external effects or be-
tions. As a result, parts of the decisions of a lifelike system       haviour change of other systems)
are about the current integration into such a constellation, re-
sulting in ’self-improving system integration’ (Bellman et al.      • This may be augmented with an estimation of the impact
(2021)). Although there is currently no integration mea-              and severity as well as a prediction of the upcoming de-
sure available, recent work suggests that such an integration         velopments.
state is probably a multi-objective function that builds upon       • Further, the self-explanation should come in a human-
metrics mentioned in the context of SASO measures (Gruhl              understandable format, i.e. using human-interpretable ter-
et al. (2018)).                                                       minology (e.g., ’Device X became too hot due to overload
   Finally, such a lifelike character obviously has implica-          that was caused by new component Y’)
tions on the way we design and operate systems. In con-
trast to current practices that take design-related decisions       • Finally, these explanations have to be generated in a
and provide corridors of freedom for the self-* mechanisms,           timely and accurate manner and become subject to a
design-time decisions themselves need to become reversible            learning process that optimises the self-explanation per
or changeable by the systems, resulting in a degree of re-            user. In particular, this can consider direct (i.e., approval
versibility (in a static manner) or changes (in the sense of          or intervention at goal level) and indirect (i.e., recognition
how strong the design has already been altered).                      and no following action by the user) feedback for optimi-
   Obviously, this list is not meant to be complete. It il-           sation purposes. The result will then be a user-specific
lustrates the need for further techniques that are suitable to        degree of explanation behaviour.
quantify the lifelike-based properties. We are convinced that
                                                                      Figure 2 illustrates the envisioned process that works as
a necessary path in lifelike research is to fill this gap with
                                                                   follows:
an integrated measurement framework that provides a basis
for comparison and assessment of the observed runtime be-          1. An observation loop is established at the macro-level that
haviour.                                                              gathers all externally visible variables of the contained
                                                                      subsystems. We aim at the maxro- or system-wide level
 III. Self-Explanations based on Macro-Level                          for explanations as we consider the autonomous subsys-
             Behaviour Assessment                                     tems as components for the overall functionality. How-
Within the last year, several contributions proposed steps to-        ever, this system boundary choice depends on the purpose
wards a self-explanation of technical systems, particularly           and the perception of the user.
focusing on aspects of self-adaptation. The most prominent         2. The resulting data is pre-processed, brought into an ap-
examples can be found in Fähndrich et al. (2013) (with a             propriate representation and analysed to determine the
Bayesian reasoning approach), Guidotti et al. (2018) (with            key figures. This includes static and dynamic indicators.
a focus on black-box classification), Bencomo et al. (2012)
(with a software engineering approach considering the satis-       3. Based on novelty/anomaly/change detection such as
faction of the requirements of a self-adaptive system), Welsh         Gruhl et al. (2021), unexplainable or unanticipated be-
et al. (2014) (also from a software engineering point of view         haviour of these key figures is recognised and assessed.
with a focus on accomplishing runtime goals), Klös (2021)            In particular, this should come up with scores for the de-
(based on an integrated design and verification framework             gree of uncertainty of the observed behaviour (with uncer-
– and the corresponding deviations), or Parra-Ullauri et al.          tainty being defined as ’explainable from previously seen
                        1) Observation                        2) Identification of                        3) Root cause
                         of key figures                        abnormal events                            determination


                                                          Dynamic measures
                                                          •   Adaptation behaviour and stability
                                                          •   Organisation behaviour
                                                          •   Evolution and flexibility
                                                          •   …                                          4) Generation of
                                                          Static measures
                                                          •   Transferability                            self-explanations
                                                          •   Variability
                                                          •   …




                                                                                             …


Figure 2: Schematic illustration of the self-explanation process using an external monitoring approach. Based on continuous
observation of static (i.e. design properties) and dynamic (i.e. time series) key indicators, unexpected or abnormal behaviour
is detected. For such events, possible root causes are identified and ranked according to their plausibility. This serves as input
to automatically generate self-explanations to the user that are human-interpretable and indicate i) What happens, ii) what the
root causes are and iii) what impact this has on the system behaviour. This may further be enriched with statements about the
expected impact or predicted future developments if possible.


   behaviour’). Such an abnormal event answers the ques-                           Challenge 1 - Metrics: The first challenge is concerned
   tion ’when should a self-explanation be generated?’                          with the metrics briefly summarised in Section II. In partic-
                                                                                ular, we have to answer the questions, which of these metrics
4. As soon as this trigger is found, the states of the con-                     is relevant? This includes answers to the question of what do
   tained subsystems and their sequences are analysed to                        metrics for the quantification of lifelike qualities look like?
   identify possible root causes. Again, this may make use                      Based on this, we have to define a mechanism to pre-process,
   of anomaly detection techniques that consider the differ-                    and represent the incoming data – which defines a standard
   ent state variables and provide uncertainty values again.                    time-series analysis problem.
   These possible root causes are collected, aggregated, cor-
   related, prioritised, resulting in an ordered list of possible                  Challenge 2 - Types of metrics and availability: As out-
   causes.                                                                      lined above, we distinguish between static and dynamic
                                                                                measures. Considering the inherent heterogeneity, we have
5. Based on this event-to-cause mapping, a self-explanation                     to find the concept of how to fuse the measures by integrat-
   is generated and provided to the user.                                       ing both, static and dynamic measures. This further results
                                                                                in questions of how to augment the pure scores, i.e. if pre-
   Please note that the integrated quantification framework
                                                                                dictions of upcoming behaviour are required and in which
to assess the system behaviour and the corresponding ex-
                                                                                resolution to allow for proactive actions.
planation loop is assumed to work at the macro-level (i.e.,
without any insight on the specific mechanisms and repre-                          Challenge 3 - Anomaly/Novelty detection: The core of
sentations of the individual subsystems), since some of the                     our concept lies in a sophisticated detection of triggers,
metrics only occur at macro-level (e.g. emergence). How-                        which is defined as unexpected behaviour of the key in-
ever, this can be turned into a hybrid system approach, where                   dicators. Technically, this should be realised in terms of
each subsystem cooperates with the system-wide loop to fil-                     anomaly, novelty or change detection techniques. Conse-
ter, augment, and customise the explanations.                                   quently, the questions arises which techniques are most ap-
   Considering this envisioned process towards automated                        propriate and how we can provide online methods. Here, we
self-explanations in lifelike systems, we face several re-                      can make use of approaches from the field of self-integrating
search challenges. In the following paragraphs, we outline                      systems (Gruhl et al. (2021)) that already focus on the de-
the most urgent ones and provide first ideas on how to solve                    sired capabilities.
them.                                                                             Challenge 4 - Root cause detection: Given that a trig-
ger for self-explanation is detected, we have to identify the                                  References
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