From Service-Oriented Architectures to Nature-Inspired Pervasive Service Ecosystems Franco Zambonelli Mirko Viroli Dipartimento di Scienze e Metodi dell’Ingegneria Dipartimento di Elettronica Informatica e Sistemistica Università di Modena e Reggio Emilia, Italy Alma Mater Studiorum – Università di Bologna, Italy Email: franco.zambonelli@unimore.it Email: mirko.viroli@unibo.it Abstract—Emerging pervasive computing scenarios require the current positions of our friends, and augmented reality open service frameworks promoting situated adaptive behaviors services to enrich what we see around with dynamically and supporting diversity in services and long-term evolvability. retrieved digital information [4]. However, the road towards We argue that this naturally calls for a nature-inspired ap- proach, in which pervasive services are modeled and deployed the effective and systematic exploitation of these emerging as autonomous individuals in an ecosystem of other services, scenarios calls for a radical rethinking of current service data sources, and pervasive devices. As an evolution of standard models and frameworks. service-oriented architectures, we present a general framework framing the concepts expressed, and discuss a number of natural II. C ASE S TUDY AND R EQUIREMENTS metaphors that we can adopt to concretely incarnate the proposed A simple case study – representative of a larger class framework and implement pervasive service ecosystems. of emerging pervasive scenarios – can help grounding our I. I NTRODUCTION arguments and sketching the requirements of future pervasive The ICT landscape, yet notably changed by the advent of services. ubiquitous wireless connectivity, is further re-shaping due to It is a matter of fact that we are increasingly surrounded by the increasing deployment of pervasive computing technolo- digital displays: from those of wearable devices to wide wall- gies. Via RFID tags and alike, objects will carry on digital mounted displays pervading urban and working environments. information of any sort. Wireless sensor networks and camera Currently, the latter are simply conceived as static information networks will be spread in our cities and buildings to monitor servers to show information in a manually-configured manner physical phenomena. Smart phones and alike will increasingly – e.g., cycling some pre-defined commercials or general inter- sense and store notable amounts of data related to our personal, est news – independently of the context in which they operate social and professional activities, other than feeding (and being and of the users nearby. However, such displays infrastructures fed by) the Web with spatial and social real-time information can be made more effective and advantageous for both users [1]. and information/service providers by becoming general, open, This evolution is contributing to building integrated and and adaptable information service infrastructures. dense infrastructures for the pervasive provisioning of general- First, information should be displayed based on the current purpose digital services. If all their components will be able to state of the surrounding physical and social environment. For opportunistically connect with each other, such infrastructures instance, by exploiting information from surrounding temper- can be used to enrich existing services with the capability ature sensors and from user profiles, an advertiser could have of autonomously adapting their behavior to the physical and ice tea commercials – instead of liquor ones – being displayed social context in which they are invoked, and will also in a warm day and in a location populated by teenagers. Also, support innovative services for enhanced interactions with the actions could be coordinated among neighboring displays, e.g., surrounding physical and social worlds [2]. Users will play an to avoid irritating users with the same ads as they pass by, or to active role, by contributing data and services and by making use adjacent displays as a single wide one to show complex available their own sensing and actuating devices. This will multifaceted information. These examples express a general make pervasive computing infrastructures as participatory and requirement for pervasive services: capable of value co-creation as the Web [3], eventually acting • Situatedness — Pervasive services deal with spatially- as globally shared substrates to externalize and enhance our and socially-situated activities of users, and should thus physical and social intelligence, and make it become collective be able to interact with the surrounding physical and and more valuable. social world and adapt their behavior accordingly. The We are already facing the commercial release of a variety infrastructure itself, deeply embedded in the physical of early pervasive services trying to exploit the possibili- space, should effectively deal with spatial concepts and ties opened by these new scenarios: GPS navigator systems data. providing real-time traffic information and updating routes Second, and complementary to the above, the display infras- accordingly, cooperative smart phones that inform us about tructure and the services within should automatically adapt to their own modifications and contingencies in an automatic way without experiencing malfunctionings, and possibly taking advantage of such modifications. Namely, when new devices are deployed or when new information is injected, a sponta- neous re-distribution and re-shaping of the overall displayed information should take place. For instance: the deployment of a big advertising display in a room may suggest re-directing there all the ads previously forwarded to the personal displays of users; the injection of a new information service could induce aggregating it with the existing ones to provide a more complete yet uniform service. In terms of a general requirement for decentralized and dynamic scenarios: • Adaptivity — Pervasive services and infrastructures should inherently exhibit properties of autonomous adap- tation and management, to survive contingencies without human intervention and at limited costs. Third, the display infrastructure should enable users – other than display owners – to upload information and services to enrich the offer or adapt it to their own needs. For instance, users may continuously upload personal content (e.g., pictures and annotations related to the local environment) from their own devices to the infrastructure, both for better visualiza- tion and for increasing the overall local information offer. Similarly, a group of friends can exploit a public display to upload software letting it host a shared real-time map to visualize what’s happening around (which would also require Fig. 1. Architecting pervasive service environments. Up: solution with a opportunistic access to the existing environmental sensors and centralized middleware server. Bottom: solution relying on a distributed set of local middleware services. to any available user-provided sensors, to make the map alive and rich in real-time information). In general, one should enable users to act as “prosumers” – i.e., as both consumers of personal projection systems to make any physical object and producers – of devices, data, and services. Not only become a display, or of eyeglass displays for immersive per- this will make environments meet the specific needs of any ception and action. While this can open up the way for brand specific user (and capture the long tail of the market), but new classes and generation of services to be conceived and will also induce a process of value co-creation increasing deployed, it also requires that such evolution can be gradually the overall intrinsic value of the system and of its services accommodated without harming the existing infrastructure and [5]. If the mentioned real-time map accesses some sensors in services. As a general requirement: unconventional ways to better detect situations around, this • Eternity — The infrastructure should tolerate long-term adds value both to such sensors and to all existing and future evolutions of structure, components, and usage patterns, services requiring situation recognition. In terms of a general to accommodate the changing needs of users and techno- requirement: logical evolution without forcing significant and expen- • Prosumption and Diversity — The infrastructure should sive re-engineering efforts to incorporate innovations and tolerate open models of service production and usage changes. without limiting the number and classes of services provided, and rather taking advantage of the injection of III. F ROM S ERVICE -O RIENTED A RCHITECTURES TO new services by exploiting them to improve and integrate NATURE -I NSPIRED P ERVASIVE S ERVICE E COSYSTEMS existing services whenever possible, and add further value Could the above requirements be met by architecting per- to them. vasive service environments around standard service-oriented Finally, beside short-term adaptation, in the longer-term architectures (SOA) [6]? Yes, to some extents, but the final any pervasive infrastructure will experience dramatic changes result would be such a scramble of SOA to rather suggest related to the technology being adopted, as well as in the re-thinking from scratch the architecture and its founding kinds of services being deployed and in their patterns of usage. principles. For instance, a display infrastructure will somewhen integrate more sophisticated sensing means than we have today and A. Centralized SOA Solution will possibly integrate enriched actuators via which to attract In general, SOA consider the inter-related activities of user attention and interact with them. This can be the case service components to be managed by various infrastructural (middleware) services such as: discovery services to help indirectly influence each other (being their actions possibly components get to know each other; context services to help dependent of such tables), as in a sort of shared dataspace components situate their activities; orchestration services to model. This also induces specific orchestration patterns for coordinate interactions according to specific application logics; components, based on the local logics upon which the mid- and shared dataspace services to support data-mediated inter- dleware relies to distribute information and events among actions. To architect a pervasive display environment in such components and to put components in touch with each other. terms (Figure 1-up), one has to set up up a middleware server A problem of this distributed architecture is to require in which to host all the necessary infrastructural services to solutions both to tune it to the spatial characteristics of the support the various components of the scenario, i.e., displays, scenario and to adaptively handle contingencies. The logics of information and advertising services, user-provided services, allocation of middleware servers (i.e., one server per display) sensing devices and personal devices. derives naturally only in a static scenario, but the arrival and Such components access the discovery service to get aware dismissing of displays requires the middleware servers to react of each other. However, in dynamic scenarios (users and by re-shaping the spatial regions and the service components devices coming and going), components are forced to con- of pertinence of each of them, also correspondingly notifying tinuously access (or being notified by) the discovery service components. To tackle this problem, the actual distribution to preserve up-to-date information—a computational and com- of middleware servers should become transparent to service munication wasting activity. Also, since discovery and inter- components—they should not worry about where servers are, actions among components have to rely on spatial information but will simply act in their local space confident that there (i.e., a display is interested only in the users and sensors in its are servers to access. Moreover, the network of servers should proximity), this requires either sophisticated context-services be able to spontaneously re-organize its shape in autonomy, to extract the necessary spatial information about components, without directly affecting service components but simply adap- or to embed spatial descriptions for each component into its tively inducing in them a re-organization of their interaction discovery entry, again inducing frequent and costly updates to patterns. keep up with mobility. To adapt to situations and contingencies, components should C. Nature-inspired Ecosystems be able to recognize relevant changes in their current environ- Pushed towards a very dense and mobile network of nodes ment and plan corrective actions in response to them, which and pervasive devices, the architecture will end up being again require notable communication and computational costs perceivable as a dense distributed environment above which for all the components involved. Alternatively, or complemen- a very dynamic set of spatially-situated components discover, tary, one could think at embedding adaptation logics into some interact, and orchestrate with each other. This is done in specific server inside the middleware (e.g., in the form of terms of a much simplified logics, embedded into the unique autonomic control managers [7]). However, such logics would infrastructural service, subsuming the roles of discovery, con- have to be very complex and heavyweight to ensure capability text, dataspace, and orchestration services, and taking the of adapting to any foreseeable situation, and especially hard form of a limited set of local rules embedded in the spatial for long-term adaptivity. substrate itself. That is, we would end up with something that notably resembles the architecture of natural ecosystems: a B. Decentralized SOA Solution set of spatially situated entities interacting according to well- To reduce the identified complexities and costs and better defined set of natural laws enforced by the spatial environment match the characteristics of the scenario, one could think at a in which they situate, and adaptively self-organizing their more distributed solution, with a variety of middleware servers interaction dynamics according to its the shape and structure. deployed in the infrastructure to serve, on a strictly local basis, Going further than architectural similarity, the natural only a limited portion of the overall infrastructure. For instance metaphor can be adopted as the ground upon which to rely to (Figure 1-bottom), one could install one middleware server for inherently accommodate the requirements of pervasive service each of the available public displays. It will manage the local scenarios. Situatedness and spatiality are there by construction. display and all local service components, thus simplifying Adaptivity can be achieved because of the basic rules of the local discovery and naturally enforcing spatial interactions. game: the dynamics of the ecosystem, as determined by the Adaptation to situations is made easier, thanks to the possi- enactment of laws and by the shape of the environment, can bility of recognizing in a more confined way (and at reduced spontaneously induce forms of adaptive self-organization be- costs) local contingencies and events, and of acting locally side the characteristics of the individual components. Accom- upon them. modating new and diverse component species, even towards a With the adoption of a distributed solution enforcing local- long-term evolution, is obtained by making components part ity, the distinction between the logics and duties of the differ- to the game in respect of its rules, and by letting the ecosystem ent infrastructural services fades: discovering local services dynamics evolve and re-shape in response to the appearance and devices implies discovering something about the local of such new species. This way, we can take advantage of context; the dynamics of the local scenarios, as reflecting in the the new interactional possibility of such new services and local discovery tables, makes it possible to have components of the additional value they bring in, without requiring the • Species — This level includes a variety of components, belonging to different “species” yet modeled and com- putationally rendered in a uniform way, representing the individuals populating the ecosystem: physical and virtual devices of the pervasive infrastructure, digital and network resources of any kind, persistent and temporary knowledge/data, contextual information, software service components, or personal user agents. In our case study, we will have different software species to represent displays and their displaying service, the various kinds of sensors distributed around the environment and the data they express, software agents to act on behalf of users, display owners, and advertisers. In general terms, an ecosystem is expected to be populated with a set of individuals physically deployed in the environment, Fig. 2. A Conceptual Architecture for Pervasive Service Ecosystems situated in some portion of the ecosystem space, and dynamically joining/leaving it. • Space — This level provides and gives shape to the spa- individual components or the infrastructure itself (i.e., its laws tial fabric supporting individuals, their spatial activities and structure) to be re-engineered [8]. and interactions, as well as their life-cycle. Given the Indeed, nature-inspired solutions have already been exten- spatial nature of pervasive services (as it is the case of sively exploited in distributed computing [9] for the implemen- information and advertising services in our case study), tation of specific adaptive algorithmic solutions or of specific this level situates individuals in a specific portion of the adaptive services. Also, many initiatives – like those named space, so that their activities and interactions are directly upon digital/business service ecosystems [10] – recognize that dependent on their positions and on the shape of the the complexity of modern service systems is comparable to surrounding space. that of natural ones and requires innovative solutions also to Practically, the spatial structure of the ecosystem will be effectively support diversity and value co-creation. Yet, the reified by some minimal middleware substrate, deployed idea that natural metaphors can become the foundation on on top of the physical deployment context, supporting the which to fully re-think the architecture of service systems is execution and life cycle of individuals and their spatial far from being metabolized. interactions. From the viewpoint of such individuals, the middleware will have to provide them (via some API) IV. A R EFERENCE C ONCEPTUAL A RCHITECTURE with the possibility of advertising themselves, accessing The above discussion leads to the identification of a ref- information about their local spatial context (there in- erence conceptual architecture for nature-inspired pervasive cluded the other individuals around), and detecting local service ecosystems (see Figure 2). events. From the viewpoint of the underlying infrastruc- The lowest level is the concrete physical and digital ground ture, the middleware should provide for transparently on which the ecosystem will be deployed, i.e., a dense infras- absorbing dynamic changes and the arrival/dismissing of tructure (ideally a continuum) of networked computing devices the supporting devices, without affecting the perception and information sources. At the top level, prosumers access the of the spatial environment by individuals. open service framework for using/consuming data or services, Technologically, this can be realized by a network of as well as for producing and deploying in the framework active data-oriented and event-oriented localized services new services and new data components or for making new (e.g., tuple spaces [11]), spread on the nodes of the per- devices available. In our case study, they include the users vasive substrate, and accessible on a location-dependent passing by, the display owners, and the advertising companies basis by individuals and devices. Indeed, recent proposals interested in buying commercial slots. At both levels openness in the area of tuple-based coordination services for per- and its dynamics arise: new devices can join/leave the system vasive and mobile devices, such as TOTA [11] or LIME at any time, and new users can interact with the framework [12], can effectively candidate as the basic engine for and can deploy new services and data items on it. In our case reifying the space level, provided they are extended to study, we consider integration at any time of new displays and automatically re-shape the spatial domain of competence new sensors, and the presence of a continuous flow of new of each node in response to contingencies (e.g., along the visualization services (e.g. commercial advertisers) and users, lines promoted in P2P computing by content-addressable possibly having their own devices integrated in the overall networks [13]). In the case study, for instance, one could infrastructure. think at assigning one tuple space for each display, and In between these two levels, lay the abstract computational have the various displays dynamically self-configure their components of the pervasive ecosystem architecture. spatial domain of competence accordingly to geographi- cal and “line of sight” factors. of adapting, and fully translated this as a property of the • Eco-Laws — The way in which individuals (whether application level and of its dynamics. services components, devices, or generic resources) live The dynamics of the ecosystem will be determined by and interact is determined by the set of fundamental “eco- individuals acting based on their own goals/attitudes, yet being laws” regulating the ecosystem model. Enactment of eco- subject to the eco-laws for their interactions with others. laws on individuals will typically affect and be affected Typical patterns that can be driven by such laws may include by the local space around and by the other individuals forms of adaptive self-organization (e.g., spontaneous service around. In our case study, eco-laws might provide at aggregation or service orchestration, where the eco-laws plays automatically and dynamically determining to display a an active role in facilitating individuals to spontaneously specific information on a screen as a sort of automatic interact and orchestrate with each other, also in dependence reaction to specific environmental conditions, or at having of current conditions), adaptive evolution (changing conditions two displays spontaneously aggregate and synchronize reflect in changes in the way individuals in a locality are with each other in showing specific advertisements. affected by the eco-laws) and of decentralized control (to affect Although the set of eco-laws is expected to be always the ecosystem behavior by injecting new components in it). the same for a specific implementation, they will possi- bly have different effects on different species. Accord- V. M ETAPHORS ingly, their enactment may require the presence of some Beside the above architectural guidelines, what actual shape meaningful description (within the uniform modeling of can species, space, and eco-laws take in an actual implemen- individuals) of the information/service/structure/goals of tation? Identifying and validating specific solutions in this each species and of their current context and state. These direction will be a key challenge of pervasive computing in descriptions, together with proper “matching” criteria, the next years. Yet, we argue that whatever solution will most define how the eco-laws apply to specific species in likely get inspiration from one of the key natural metaphors specific conditions of the space. We emphasize that, in the already explored in the literature, or possibly extract specific proposed architecture, the concept of “semantic descrip- desirable aspects from many of them towards a new syn- tion” of traditional SOA to facilitate discovery turns into thesis. Key metaphors include physical [11], chemical [14] a concept of “alive semantic description” (dynamically and biological ones [9], along with metaphors focussing on changing as the context and state of components change), higher-level social models (e.g., trophic networks [15])—the to properly rule the dynamic enactment of eco-laws. key difference between them being in the way the species, the Practically, to be able to code eco-laws and enact them, space, and the eco-laws are modeled and implemented (see the middleware substrate should proactively mediate Figure 3). inter-component interactions, and act as an active space All the metaphors, by adhering to the proposed architec- in which to store their continuously updating semantic ture, are by construction spatially situated, adaptive by self- descriptions, so as to adaptively support the matching organization, and open to host diverse and evolving species. process triggering eco-laws in dependence of the current However, when it comes to modeling and implementing, conditions of the overall ecosystem. Technologically, different metaphors may tolerate with variable efficiency and since most tuple-based middleware systems are currently complexity the enforcement of adaptive self-organization pat- enriched with the capability of reacting to events and of terns and the support of diversity and evolution. In addition, configuring the matching process, they could well act as since the service ecosystem is here to ultimately serve us, the interaction media in which to embed and enact eco- it is necessary to analyze how and to which extent the laws. metaphors facilitate exerting forms of decentralized control over the ecosystem behavior, in order to direct its self- The proposed architecture represents a radically new perspec- organizing activities and behavior and not to lose control tive on modeling service systems and their infrastructures. over it. Ideally, a metaphor should be able to support these The typically heavyweight and multifaceted layers of SOA features while limiting the number and complexity of eco- are subsumed by an unlayered universe of components, all of laws, the complexity of individuals and their environment, which underlying the same model, living and interacting in the while keeping the infrastructure lightweight and the overall same spatial substrate, and obeying the same eco-laws—being execution efficient. the latter the only concept hardwired into the system. This rethinking is very important to ensure adaptivity, A. Physical metaphors diversity, and long-term evolution: no component, service or These consider species as sort of computational particles, device is there to stay, everything can change and evolve, living in a world of other particles and virtual computational self-adapting over space and time, without undermining the force fields, the latter acting as the basic interaction means. overall structure and assumptions of the ecosystem. That is, Activities of particles (to be practically modeled and imple- by conceiving the middleware in terms of a simple spatial mented as reactive agents) are driven by laws that determine substrate in charge of enforcing only basic interaction rules, how particles spread fields, how fields propagate and reshape we have moved away from the infrastructure itself the need upon changing conditions, and how they influence particles Fig. 3. Metaphors for Pervasive Service Ecosystems (those whose semantic description “matches” some criterion). for dynamically re-assigning information and ads to different Particles change their status based on the perceived fields, displays. and move or exchange data by navigating them (i.e., particles Physical metaphors have been extensively studied for their spread sort of data particles to be routed according to the shape spatial self-organization features, and for their effectiveness of fields). The world in which such particles live and fields in facilitating the achievement of coherent behaviors even spread and diffuse can be either a simple (euclidean) metric in large scale systems—for load balancing, data distribution, world mapped in the physical space, or a virtual/social space clustering, aggregation, and differentiation of behaviors. The mapped on the technological network. From the infrastructural conceptual tools available for controlling the spatial behavior viewpoint, a network of local tuple spaces will have to proac- and the dynamics of such systems are well-developed, most tively support the storing of local field values, the propagation of them related to acting on how fields propagate and dy- and continuous update of fields across the network, and the namically change—by which it is actually possible to exert notifications about these changes to individuals. For instance, control over the overall system behavior. On the other hand, the TOTA middleware [11] can be adopted for the implemen- such metaphors hardly tolerate high diversity and evolution. tation and management of physically-inspired distributed field In fact, to support very diverse species and behaviors (at a data structures. time and over time), eco-laws must become complex enough In the case study, we can imagine display services as masses to tolerate a wide range of different fields and propagation emitting gravitational-like fields (in the form of broadcast rules, with an increase in the complexity of the model and events or spanning trees over the network). Such fields have in burden on the infrastructure [11], that has to proactively different “flavors” (i.e., different semantic descriptions, reflect- support the propagation and continuous update of many field ing the characteristics of users around and the environment structures. conditions) and an intensity proportional to either their dimen- sion or the available display slots. Information and advertiser B. Chemical metaphors agents can behave as masses attracted by fields with specific These consider species as sorts of computational flavor, eventually getting in touch with suitable displays for atoms/molecules (again modeled and implemented as their information and ads. Upon changing conditions, the reactive agents), enriched with semantic descriptions acting structure and flavors of diffused fields will change, providing as the computational counterpart of the bonding properties of physical atoms/molecules (yet made dynamic to reflect evaporating. The spatial environment is again a computational the current state and context of individuals). Accordingly, landscape either mapped on the network topology or on the the laws that drive the overall ecosystem behavior resemble physical space. Unlike physical systems, individuals here are chemical reactions, that dictate how chemical bonding not necessarily passively subject to the sensed pheromones, but between components take place (relying on some forms of they can react to them depending on their current “mood” (e.g., pattern matching between semantic descriptions), and lead their state towards the achievement of a goal). Consequently, to aggregated, composite, and new components, and also to eco-laws are only aimed at determining how such pheromones, growth/decay of species. The world where individuals live depending on their specific flavors, should propagate and dif- is typically formed by a set of spatially confining localities, fuse in the environment. From the implementation viewpoint, intended as the “solutions” in which chemical interactions any infrastructure that can support physical metaphors can also occur and across which chemicals can eventually diffuse. be adapted to support biological metaphors, by turning fields The declarative tuple space model of TuCSoN coordination into persistent and slowly diffusing/evaporating data structures. infrastructure can support an effective implementation for In the case study, users will be represented by simple chemically-inspired interactions [14]. agents roaming around and spreading chemical signals with a In the case study, we can think of display services, of flavor reflecting their personal interests. Displays can locally information services (concerning ads and news), as well as of perceive such pheromones, and react by emitting some dif- user and environmental data as molecules. Displays represent ferent pheromones to express the availability of commercials different localities (i.e., tuple spaces) in which components and information. Advertising and information agents, by their react. Chemical rules dictate that when the preferences of side, sense the concentration of such pheromones and are a user entering the locality of a display match an informa- attracted towards the displays where the concentration of users tion/advertisement service, then a new composite component with specific interests is maximized. Displays, advertising and is created which is in charge of actually displaying that service information agents by their side, and depending on what they in that display. Concurrently, in each locality, catalytic com- have displayed so far, can also emit additional flavors of ponents can be in charge of re-enforcing the concentration of pheromones, to store memory of past events. The persistence specific information or of specific information/advertisements, of pheromones can also be exploited by additional components reflecting the current situation of users. Also, localities can be that, by moving from display to display, create pheromones open to enforce chemical bonds across displays, so that high- trails as a basis for more global strategies—like identifying activity of advertisement reactions on a display can eventually routing paths that advertiser agents use to globally find the propagate to neighbors. best displays to exploit. Chemical metaphors can effectively lead to self-organizing Biological metaphors appear very flexible in efficiently structures like local composite services and local aggregates. enabling the spatial formation of both localized and distributed As in real chemistry, chemical computational metaphors can activity patterns, and have a variety of applications [9]. The accommodate an incredible amount of different components problems of accommodating diversity and evolution that affect and composites with a single set of basic laws. In practice, physical metaphors are here notably smoothed. In fact, an this means that it can tolerate an increasingly diverse and increase in the variety of pheromone flavors (to support evolving set of semantic descriptions for components without diversity and evolution) can be handled with less overhead affecting basic eco-laws and without increasing the burden to by the infrastructure, since pheromones (unlike fields) rely the infrastructure. As far as control is concerned, one can think on local diffusion and slow evaporation dynamics. On the at using sort of catalyst or reagent components to engineer negative side, since the mechanisms of morphogenesis and and control (in a fully decentralized way) the dynamics and self-organization in actual biological systems are not fully the behavior of the ecosystem. A limitation of the chemical understood yet, it can be consequently hard to understand how approach is that it typically relies on activities taking place to enforce control in their computational counterparts too. within a locality or at least across neighboring ones via local diffusion [14], making it hard to naturally and easily enforce D. Social metaphors distributed self-organized behaviors, like creating a complex These focus on biological systems at the level of animal and distributed aggregation of components. species and of their interactions [15]. Individuals are sorts of goal-oriented animals (i.e., agents) belonging to a specific C. Biological metaphors species, that are in search of “food” resources to survive and These focus on biological systems at the scale of individual prosper, and that can represent in their turn food to others organisms, or of colonies of organisms like ants. The species (both aspects reflecting in some proper semantic descriptions). are therefore either simple cells or animals acting on the basis Pure data items and resources can be abstracted as sorts of of simple goals like finding food and reproducing (to be mod- passive life-forms (i.e., vegetables). The eco-laws determine eled and implemented in terms of simple goal-oriented agents). how the resulting “web of food” should be realized, namely, As in physical systems, interactions take place by means of how animals search food, eat, and possibly produce and signals of various flavors (i.e., chemical pheromones) spread reproduce, thus influencing and ruling the overall dynamics by individuals in the environment, and slowly diffusing and of the ecosystem and the interaction among individuals of different species. Similarly to chemical systems, the shape identified to incorporate the key features of the existing of the world is typically organized around a set of localities, metaphors into a unifying general-purpose one. i.e., ecological niches, yet enabling interactions and diffusion In addition to the key problem of identifying suitable of species across niches. From the implementation viewpoint, metaphors, the widespread deployment of nature-inspired per- reactive tuple space models [12] can be effectively adopted vasive service ecosystems requires methodologies and tools towards the realization of a supporting infrastructure, where for their engineering, proper security mechanisms and policies, the possibility for the tuple space to enforce control over all and means to integrate the approach with the legacy of current interactions can be used as a mean to rule the food-web-based SOA systems. 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