Review: Applying the Web Ontology Language to management information definitions

Jorge Vergara et al proposent d'utiliser le langage des ontologies "Web Ontology Language" OWL pour donner plus de sémantique et d'expressivité aux modèles de données.

Ils proposent d'utiliser OWL pour les raisons suivantes:

1. OWL est basé sur du RDFS et RDF
   
2. RDFS et RDF sont basés sur du XML et offrent un ensemble structuré de termes: hierarchie des classes, domaine et contraintes.
   
3. XML (eXtended Markup Language) est largement utilisé comme format d'échange, de représentation et d'interprétation d'information. L'utilisation d'XML est favorisée par l'existence d'un grand nombre d'outils et librairies qui faciliteront la validation (DTD) et le traitement des informations. En plus , XML peut être utilisé afin de représenter l'information autrement dans un scénario d'interopérabilité des protocoles d'administrations.

Jorge insiste sur le besoin d'introduire de la sémantique dans les data model existants afin d'arriver à passer de l'un à l'autre facilement. Actuellement, le passage entre 2 data models se fait par du recast autrement dit un mapping syntaxique plutôt manuel.
L'idée est de traduire les data models en OWL.
En effet, les data model actuels sont vu comme des ontologies 'light" puisqu'ils présentent entre autre un ensemble de concepts (class, attributs etc) et d'instance de concepts ainsi que des relations (sous-class, association de class etc). Cependant ces data models ne sont pas assez expressifs, pas de possibilité d'écrire des axiomes.

Or OWL est un langage d'ontologie général et lui manque quelques aspects pour pouvoir traduire les models de données en OWL. Les droits d'accès (Lecture, écriture) , les unités de mesures (Bit/seconde) ainsi que les valeurs par défaut pour les attributs. Les auteurs étendent OWL avec ces aspects tout en se basant sur du RDFS. (voir Fig, clic pour agrandir)




Conclusion:
Cet article présente une approche pour une interopérabilité entre data model tout en se basant sur OWL. Ce langage est basé sur du RDFS qui est capable de décrire un data model par des class, propriété, hiérarchie, domaine et types.
RDFS lui même est basé sur du XML ce qui facilite l'échange et le traitement d'information par des outils déjà existants.
Des extensions ont été ajoutées à OWL (en utilisant RDFS) afin d'arriver à traduire tous les aspects d'un modèle de donnée vers OWL.
Ils proposent également de formuler avec du SWRL (Semantic Web Rule Langage) des règles et des axiomes (plus de détails bientôt).

Review: Design considerations for a network of Information

In this position paper they insist on the fact that the Internet has to be reshaped and be focused on data instead of endpoints, in order to have a data centric network or network of information.
According to Jacobson [1], the first generation of the network dealt with connecting wires. The second one focused on end nodes hosting data while the third generation should refocus on what humans care the most about Information.

Their information models distinguish between 2 main objects:
Data Objects (DO): are the actual bit-patterns that contain the information: such as file, phone call, video, web page, a song(Beethoven's 9th symphony) etc. These data objects can be divided into "chunks" smaller pieces in order to simplify the transfer.
Information Objects (IO): holds semantic information and meta-data related to data objects, such as Beethoven's 9th symphony is an mp3 file encoded with 128kbps, IOs can be composed of other IOs or directly pointing to one or multiple DOs. An IO can represent the Eiffel tower and point to DO like pictures, a wiki page or service to buy tickets, etc.

Versioning and Revocation:
Since some information is frequently changing such as news papers. An IO can represent today's version, however the IO should adapt dynamically by binding to another DO (web page) the next day, and so on for the IO pointing to yesterday's news.
They suggest that objects invalidate themselves in order to conserve consistency. After an amount of time, objects should be recertified before it can be used. By applying this technique, they maintain consistency due to disconnected operation during information update of other replicas for example. DO can be deleted same way when no certification is given.

Security considerations:
Security in today's architecture is based on confidence (Encryption keys) of the host delivering the object, they propose to reshape security conventions so we can handle secured data instead of secured tunnels.
Integrity and authenticity is directly tied to object's names which means there would be a cryptographic relation between the name and object such as self-certifying names. However to enable off-line verification, DO must carry private keys which can be compromised. Another approach is to assign precomputed signatures to objects. It remains a research field.

Name resolution(NR):
Data objects are retrieved based on their unique identity (UID). NR starts with locating the object in the network then routing forwards the object retrieval query to its storage location and finally the DO is sent to the requesting client.
The naming resolution resolves an UID into one or more locations and should work on global and local scale by cooperating between NR systems for example. They show the side effects if ID/address split mechanism is adopted with the following example, if a laptop hosting numerous Data Objects moves its location then all Data objects location changes too. This will lead to huge number of updates in the NR system.
The NR system will be influenced by the characteristics of namespaces. They would like to adopt flat names which respects the non right of ownership and other characteristics revealed by [2].
Off course, using flat names prevents the use of hierarchical names spaces and systems like DNS.
DHT based solutions are promising since the are decentralized, scalable, self-organized and don't need central structure. However when going globally DHT uses flat names hence non hierarchical names which prevents cooperation with other systems.

Routing:
Addressable entities are still increasing and will reach millions even billions in few years with the emergence of sensor networks, Internet of things, growing data etc. They claim that routing research are not encouraging according to [3] (will be reviewed later). Hence, they ll investigate the efficiency of name based routing which integrate both resolution and retrieval paths. Name based routing will locate DO based on their ID by transforming the ID directly into a path without going through ID-address transition. Other techniques such as LLc and NodeID are to be investigated also (Soon will be reviewed).

Storage:
The information network can be implemented following two different models:

• Network based storage model where storage resources are provided by the network infrastructure, like dedicated storage servers.

• Network managed storage model where network nodes control portions of storage memory of users connected to the network. Users will be able to decide what DO goes public or be shared only with friends etc.

Search:
Search systems are expected to go far beyond text match search, such as semantic search or even search functionality based on GPS position, location positioning. For example when a picture of Eiffel tower is taken, a search mechanism will handle the identification of the monument based on GPS or other techniques and points to DO related informations such as web page, history etc.

This position paper gives many ideas and anticipations about the future Internet architecture and reveals the weakness in the current addressing system. They distinguish between DO and IO and argued that a network of information needs a scalable naming system supported by an efficient routing system.

References:
1 - V. Jacobson, M. Mosko, D. Smetters, and J. Garcia-Luna-Aceves. Content-centric networking. Whitepaper, Palo Alto Research Center, Jan. 2007.
2 - M. Walfish, H. Balakrishnan, and S. Shenker. Untangling the web from DNS. In NSDI’04: Proc. 1st Symp. on Networked Systems Design and Implementation, San Francisco, CA, USA, 2004.

Link to the article

Review: RFC 4941 Privacy Extensions for Stateless Address Autoconfiguration in IPv6

RFC 4941 reveals privacy issues related to IPv6 stateless auto configuration.

The IPv6 stateless auto configuration allows hosts to generate IP addresses without the need of a central node to coordinate and distribute unique addresses. The mechanism allows to generate a unique IP address by using the IEEE interface identifier. Actually the interface identifier is generated based on address identifier such as a MAC address which is supposed to be unique, a characteristic guaranteed by the constructor/manufacturer of the network card.
Using a unique interface identifier allows nodes to generate unique IPv6 addresses. The Node adds the network prefix to the interface identifier in order to obtain a 128 bit unique (local or global) address.
Consequently, when a node moves to another network the prefix is the only changing part in the IPv6 address since the interface identifier is always the same and unique.
This unchanging part of the IP address allows for tracking and user localization which violates privacy. ( An employee is at home?, active?, with whom he is communicating? etc).
This privacy problem occurred in the IPv6 and did not exist in the IPv4 which assigned IP addresses independently from the interface identifier.

Any possible Approaches?

• Use DHCPv6 to assign and manage addresses. Those addresses are also temporary and never changed. RFC 4941 claims to propose a similar DHCPv6 approach when using temporary addresses.
• Change the interface identifier portion of the address over time and generate new addresses from the interface identifier.
• Caller ID approach: Many machines function as clients and servers. When acting as a server the machine would need a DNS name. The privacy issue appears when the machine is acting like a client and its identity is revealed. (The similarity with the caller ID approach is when a user lists his telephone numbers publicly but disable the display of its number when initiating calls.)
  

RFC 4941 proposal:
Their approach proposes the generation of Temporary addresses, a pseudo-random sequence of interface identifiers using the MD5 hash. These addresses would be used for a short period of time. New temporary addresses will be generated to replace the expired ones. Nodes concerned about privacy may use different interface identifiers on different prefixes.

Generation of Randomized Interface Identifiers:
They propose to use 2 approaches in order to generate randomized interface identifiers.

• The first requires a 64 bit stable storage for generated temporary addresses, so the new generated address is based on the previous one. This technique prevents two nodes of generating the same random number.
• The non stable storage technique will use configuration parameters like user ID, serial numbers with a randomized data and an MD5 algorithm is order to generate random numbers.
• Alternate approaches can be used like CGA (Cryptographically Generated Addresses) to generate a random interface ID based on the node's public key. The purpose is to prove ownership of an IPv6 address and prevents stealing and spoofing of addresses. However this technique requires that a node holds a public key. The node can still be identified by its key (transactions etc). The process is intensive and discourages frequent regeneration. (Especially on low cost machines).
  

However, every time a node generates a value it should checks that the address in not reserved for particular usage or already assigned. If so, the node should repeat the process of generating random interface identifiers. The node also generates temporary addresses of every public address created. New Temporary addresses should be generated to replace expired ones.

The use of temporary addresses is an approach proposed to resolve privacy issues, however this solution have the following impacts on the Internet:

• The widespread use of temporary addresses complicating the flexibility of generating global unique addresses from interface identifiers since for each generated address DAD should be applied.
• Clients having their addresses changing over time will make packet tracking more difficult and so debugging when unknown behaviors occurs. Hence the packet's source cannot be determined if it is from one machine or multiple ones.
• Some servers refuses access to clients for which no DNS names exists. Temporary addresses are not registered.
• How to distinguish in a large network with a high rate of changing temporary addresses between the new generated addresses and spoofed addresses.

We can see clearly that stateless auto configuration generates addresses without the need of a central node and no need to apply DAD. However this unchanging part is causing privacy issue and permits identification and node tacking across the Internet due to the prefix modification when entering another network.
This prefix modification is the result of the hierarchical nature of the Internet addresses to facilitate routing and delegate address management between organizations. An unstructured architecture will hide the topology of the network but will add more burden on routers in order to transfer and deliver packets.
A new naming and addressing approach should make a good balance between simplicity and flexibility in generating global unique addresses in a distributed, self manner and providing privacy hence not exposing identity and node's location.

Link to the RFC

Review: 6LowPAN

Why IPv6 can’t be applied directly on LowPANs?
6LoWPAN defines IPv6 protocol over Low power Wireless Personal Area Networks.
LowPAN devices uses IEEE 802.15.4 radios. In order to understand why we
can’t use IPv6 directly on top of LowPAN devices let’s list the characteristics of such
devices [2]:

• Small packet size. 81 bytes for data packets in the networking layer. (The maximum physical layer packet is 127 bytes, consequently the maximum frame size at the media access control layer is 102 octets. 21 bytes at maximum are usedfor securing link-layer communications).
• Support for both 16-bit short or IEEE 64-bit MAC addresses.
• Low cost devices: low bandwidth with data rates of (250 kbps, 40 kbps, 20 kbps) for (2.4 GHz, 915 MHz, 868 MHz). Low power typically battery dependent. Low processing and storage capabilities (8KB RAM, limited buffering, etc).
• Topologies include star and mesh operation.
  
• Large number of devices expected to be deployed.

The main problems with IP for LowPANs are the following:
The term Maximum Transmission Unit (MTU) refers to the size (in bytes) of the largest PDU that a given layer of a communications protocol can pass to other layers. A higher MTU brings greater efficiency because each packet carries more user data than protocol overheads. Large packets can occupy a slow link for some time, causing greater delays to following packets and increasing lag and minimum latency.
IPv6 protocol uses 128 bits IP address and a header of 40 bytes long. The MTU is at least 1280 bytes in order to maximize the efficiency of the transmission ((useful data)/(overhead data)).
LowPAN devices supports small packets with 81 bytes available for the networking layer and above. Using IPv6 on IEEE 802.15.4 leaves only 41 bytes for transport and applications layers. This is obviously not enough for data exchange, packet fragmentation and reassembly is needed but will use even more bytes. An IP header compression is needed.
Since large number of devices will be deployed, address auto configuration is attractive because it will reduce the overhead between devices. There is a need for a method to generate and assign an Identifier from the EUI-64 bits to a LowPAN device.
Routing protocols in mesh and star networks must be adapted to a small overhead. LowPAN devices have limited resources (memory, bandwidth, CPU, energy), processing 128 bits addresses and large headers will decrease the system’s efficiency and increase data treatment latency.

Why use IP based protocol in LowPANs?
The benefits of using IP based networks are the following [1][2]:

• The hierarchy of naming and addressing in IP networks which simplify the connectivity model.
• IP-based technologies already exist, are well-known, and proven to be working.
  
• IP networking technology is specified in open and freely available specifications.
  
• Use existing tools for diagnostics, management, and debugging of IP networks instead of designing and developing new ones.
• IP-based devices can be connected easily to other IP-based networks, without the need for intermediate entities like translation gateways or proxies.
  

Addressing Modes
IEEE 802.15.4 uses IEEE 64 bit and 16 bit addresses. Short addresses are assigned by a PAN coordinator during an event which means that validity and uniqueness of such addresses are limited by the lifetime of the association, failure of the coordinator, etc [3].
For short addresses (16 bits), a pseudo 48 bit address is formed by concatenating 16 zero bits to the 16 bit PAN ID (Personal Area Network). If no PAN ID assigned then 16 bits of zeros are used and the resulting concatenation is a 32 bits address. These 32 bits are concatenated with the short address in order to obtain a 48 bit address.
From a 48 bit address, a 64 bit interface identifier is formed as in [5] and [6] by adding 0xFFFE in the middle of the 48 bits (24 bits,0xFFFE,24bits). IPv6 local addresses are formed using the 64 interface identifier by appending the prefix FE80::/64. (0xFE80::EUI-64) or global addresses based on information advertised by routers [7].
Routers are the link between IP and LowPAN networks, those routers will handle address transition.

Header types
6LowPAN proposes specific header encoding and compression mechanisms to adapt IPv6 into IEEE 802.15.4 frames. Separating headers will reduce overhead. If a device is sending short packets directly to another node it does not pay for extra fields such as Mesh networking or fragmentation. The overhead reduction is an energy saving.
The header types are the following:

• The Dispatch Header (1 byte), define the type of header to follow. The dispatchheader is identified by the first two bits set to either 00 (non-6LowPAN frames)or 01. The remaining 6 bits indicate if the following field is an uncompressedIPv6 header or an HC1 header (IPv6 compressed header). To accomplish compression[1] the protocol uses a combination of the following facts: the low order64 bits of an IPv6 address (the link local address) can be the device’s MAC address,the 802.15.4 frame carries these MAC addresses, a number of the fields inthe IPv6 header are static.Combining all of these features allows the protocol to compress the standard 40 byte IPv6 header down to just 2 bytes (including the HC1 Header byte) for most intra-PAN unicast communication where source and destination addresses are deleted and generated from Link level frames (IEEE 802.15.4). All of the rest of the fields can be reconstituted without any state information at any of the receiving or intermediate nodes. Additionally by assigning the link local address to the device’s MAC address 6lowpan can use Stateless Address Auto configuration(Zero-conf) and eliminates the need to infrastructure servers like DHCP servers.
• The Mesh Header (4 bytes) is used to encode the hop limit and the source and destination of the packet. It includes two single bit fields to indicate if the originating
  or final address is a short or long address. The “hops left” field is a 4 bit
  field used to limit the number of intermediate hops between the source and destination.
  The value of 0xF was reserved to indicate that an extra byte is included
  allowing for network depths of up to 255 hops.
• The Fragmentation Header (4 bytes for the first fragment and 5 bytes for subsequent
  fragments) supports the fragmentation and reassembly of frames larger
  than the size of the 802.15.4 frame.

Today there is at least 6 implementations of 6LowPAN on multiple 802.15.4 radio platforms. The working group is still continuing to investigate the areas of neighbor discovery: IPv6 network prefix, local routers and other network configurations parameters.
The area of service discovery to locate other sensors and controllers and higher layer services.
Is it a good choice to push further IP based protocols to other areas such as LowPAN while efforts increases to redesign the Internet?
Should we inherit the limitation of IP which merges between naming and addressing to LowPANs?
What about cross-layering violation while compressing Ipv6 headers and regenerating source and destination address for Link level frames? According to the OSI scheme, Layers should be independent and unable to understand other layer’s data.
Even though in some cases header compression is efficient (with layer violation) other compressions remains unoptimized in LowPAN. Additional work should push routing protocols and reduce overhead of such protocols.

References:
1. The 6LoWPAN Architecture, Geoff Mulligan and 6LoWPAN Working Group, EmNets '07: Proceedings of the 4th workshop on Embedded networked sensors
2. RFC 4919: IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals.
3. RFC4944 - Transmission of IPv6 Packets over IEEE 802.15.4 Networks
4. 6LoWPAN: Incorporating IEEE 802.15.4 into the IP architecture Internet Protocol
for Smart Objects (IPSO) alliance.
5. RFC 2464: Transmission of IPv6 Packets over Ethernet Networks
6. http://technet.microsoft.com/en-us/library/cc736439(WS.10).aspx
7. RFC 4862: IPv6 Stateless Address Auto configuration

Review: SENS - a Scalable and Expressive Naming System using CAN Routing Algorithm

This paper proposes a Scalable and Expressive Naming System (SENS) based on CAN routing algorithm. SENS is a descriptive naming scheme that uses a tuple of attribute/value pairs to name each resource. A resource such a computer is named as ( String OS= "Linux", string CPU-name = "Pentium 4", etc). Those informations are stored at a large number of name servers (NS).

Their design claims to achieve scalable and efficient resource information distribution and retrieval. SENS handles exact (MEMORY = 512 MB) and multi-attribute range queries (MEMORY > 512 MB) with small overhead as well as load balancing.

DESIGN OF SENS:
Mapping resource names to resource IDs:
A resource ID is considered as a set of d coordinates of a point in the d-dimensional resource ID space. (In the example below d = 6). A resource name is mapped to a resource ID by assigning the hash value of each attribute/value (a/v) pairs of the resource name to a coordinate value of the resource ID. Name servers are responsible for resource ID sets just like in the CAN system.
Ha is a function that uniformly hashes every attribute from 1 to d and Hv hashes every attribute value in a [1, 2^(m-1)] interval where m is the maximum size of coordinate value in bits.












If multiple attributes in a resource name are hashed to the same value Ha (attr i) = Ha (attr j) then the corresponding attribute values will be mapped to multiple coordinate values in the same dimension. This means that resource names are mapped to multiple resource IDs which are distributed on NSs.


Their mapping scheme is not injective, several resource names can be mapped to the same resource ID. Consequently resource ID is not a unique identifier of resource name, in order to identify a resource, the resource_ID (resulting form Hash) and its name are required to uniquely identify a resource.

In the case of numerical attribute values, a locality preserving hashing function is used. Such hashing function is defined as if (val1 > val2) then (Hval1 > Hval2). the main purpose behind using a locality preserving hashing function is to deal with range queries, in fact it ensures that a resource ID will be in a interval of resource IDs between a min and max value. By doing this they limit the number of NSs responsible for a query range.

If the attribute/value pairs number is lower than d then the resource ID is filled with zeros.
However when the attribute/value pairs number is higher than d then the set of attributes should be divided to multiple sets of attributes which corresponds to multiple resource names. (this aspect of fragmentation is not treated in this paper).

Resource Information Distribution:
Since their scheme is CAN based, zones are assigned to NS, consequently each NS manages resource information according to the resource ID.
In the case of a resource name mapping to multiple resource IDs. If the NS is responsible for several resource IDs of the same resource, only one copy in maintained at the NS. When resource IDs belongs to different zones i.e. different NS, they use a multicast routing algorithm based on Spanning Binomial Trees. Their algorithm sends minimum amount of messages to deliver information to a NS.
Resource IDs corresponding to a resource name construct a hypercube in the resource ID space according to this article (Optimum Broadcasting and Personalized Communication in the Hypercube) . (They don't explain how the hypercube is built, so further reviews will detail the construction algorithm of hypercubes).


The registration message containing information of the resource is first delivered to the NS responsible for the resource ID created from the lowest values of each resource IDs coordinates. (In this example root node is (0.0.0)). This NS becomes the root node and forwards the message to its descendants according to the tree. Those descendants also will forward the registration message to their descendants according to the tree. etc

Query resolution:
SENS supports:

• Exact queries: A query host sends a message to a NS which will map the query resource name to resource IDs and select the nearest destination resource ID. The message arrives to destination using the CAN routing algorithm. The NS responsible for the resource ID will lookup its database to find the queried information and send it back to the initial NS (the one first queried by the host).

• Range queries, in the case of a range query it will be limited by the hash values of the upper and lower limit of the queried value ranges in each dimension. When a host sends a range query message to a NS, the latter will map the query range to a range query segment in the resource ID space. A query message will be broadcasted to all NSs whose zones overlap the segment. They propose a broadcasting algorithm based on the SBT and hypercube in order to reduce the number of messages broadcasted. (Further details will be added once I read the article that treats the hypercube and SBT formation).

Related works:
This article propose a more expressive naming scheme than DNS which offers a value-limited resource name space without the possibility to realize the range query.
Other systems such as the Intentional naming system uses a descriptive name space based also on attribute/value pairs. The message routing for a name query is realized by look up of the query name on forwarding tables. Main limitation of such systems is scalability since the forwarding tables will grow with the number of resource names.
DHT-based routing protocols like Chord, CAN achieve a scalable and efficient lookup by hashing a resource name to a DHT key. Range query is the limitation of such systems, a query may spread to the hole DHT key space.
Other systems proposes range queries like MAAN where nodes are responsible for attribute values of an attribute in the query range. The node responsible for the attribute/value pairs (String OS = "Linux") must keeps information related to Linux OS. The main limitation is load balancing since popular attribute/value pairs may appear in resource names with high probability.

SENS is naming system capable of handling resource information with exact and multi-attribute range queries. They propose a multicast/broadcast algorithm to deliver/retrieve information.
However some issues remains unclear:
Several resource names might be mapped to same resource ID and the unique identification is done by resource ID and resource name. Is it enough to uniquely identify a resource? Is it possible to map 2 different resource names having same attribute values in common into the same resource ID? In 2005 Xiaoyun Wang and Hongbo Yu achieved collision on purpose in the MD5 hashing algorithm (2 different values were hashed to same ID).
Is SENS trying to merge between search engines and DNS-like systems?
Do we really need to merge between such systems? is it faster ? More reliable? More scalable ?
Is it a good approach when a resource is mapped to many resource IDs? Having multiple IDs will accelerate routing and finding the nearest ID? What if we mapped essential and important data to multiple IDs and restrained non important data to a single resource ID? How to design such a ranking system to classify data according to it's importance?
What if I updated my RAM from 512 MB to 1024 MB, how SENS manages such updates?
Is space partition efficient? when a node joins the system, a lot of information is handled to the new joining node ? Consequently huge messages are transmitted to the new node.

Link to the article

Review: Toward a search architecture for software components

This paper proposes a design of a component search engine for Grid applications.
With the development of the component based programming model, applications are going to be more dynamically formed with the associations of components. Developers should be able to reuse already developed components that matches their needs. To do so, a component search engine seems to be essential.
The component search for Grid applications offers two facilities:

1. Developers will be able to find the best component for their need.
2. The framework can replace a malfunctioning or a slow component dynamically (at run time). The application should be able to decide the best component to be replaced with the malfunctioning.
   

They assume that open source Grid applications will appear and software components can be found on portals. These components will be ranked according to their usage, the more a component is used by applications the more important it is considered. This raking will establish a trust index. This approach is used by Google to rank the pages and improve search results.

One of the related works:
Agora components search engine supports the location and indexing of components and the search and retrieval of a component. Agora discovers automatically sites containing software components by crawling the web (Google's web crawler), when it finds a page containing an Applet tag, it downloads and indexes the related component. Agora supports JavaBeans and CORBA components. The database search is keyword based refined by users.

Workflows:
A workflow can be described as a process description of how tasks are done, by whom, in what order and how quickly.
Workflows are represented with low level languages such as BPEL4WS which requires too much user effort to describe a simple workflow.
Other high level language and Graphical User Interface on top of BPEL4WS are being introduced/build that generates BPEL code.

Their approach is workflow based: components can be adapted and coordinated through workflows. Applications should be able to choose and bind with other components from different sources on the Grid. Such applications searches first in its own local repository for components previously used or installed and uses a search engine to find suitable components.

The application development process can be divided into 3 stages:

1. Application Sketching is when developers specifies: (1) An abstract workflow plan containing the way information passes through the application's parts. (2) A place-holder describing the functions and operations to be carried out. This description will help finding a list of suited components.
2. Components discovering is based on 2 steps: First they resolve the place-holder query by searching in the local repository. If a suitable component is found locally than an identifier of this component is returned to the application. Second, If no component was found, a Query session is started on remote sites. A list of ranked components is returned and refined by user specifications.
3. Application assembling is the binding phase. Data or protocol conversion are often needed due to the heterogeneous input/output between components (string to array of double conversion etc).
   

GRIDLE is their component search engine: Google like Ranking, Indexing and Discovery service for a Link-based Eco-system of software components. The main modules are the following:

1. The Component Crawler is like a Web Crawler, it retrieves new components and updates links (bindings) between components and pass the results to the indexer.
   
2. The Indexer will build the index data structure of GRIDLE. Characteristics and meta data associated to the component should be carefully selected to be indexed. Actually the meta information associated to components will help retrieve the suited one. Such Meta data can be: (1) Functional information like interfaces (published methods, names, signatures) and runtime environment. (2) Non functional information such as QoS and textual description. (3) Linking information to other components.
   
3. The Query Analyzer resolves the queries on index basis, it uses a ranking module to retrieve the most relevant components, the search will be refined by the user.
   

To this stage, I don't have advanced knowledge in such systems and search engines but I find this approach interesting since the world of component development is emerging.
In the near future, thousands of components will be developed and ready to use. One of the main reasons of the wide adoption of the component based programming model is the ability to reuse already developed components and save time during the development process. A search engine seems to be necessary in order to find and locate suitable components.
Some issues in their approach remains unexplained or not clear such as:

• Components will be updated , deleted, added, so how to determine the crawler iteration frequency in order to update the indexing?
• The same question appears when dealing with Component binding, since the model is inspired from Web pages, I think that components are more dynamic when it deals with binding with other components. Bindings will dynamically (on runtime) appear/disappear when replacing a component, how to maintain the ranking of a component? What is the frequency of the component ranking algorithm ?
• In their approach, first they search locally for a suited component. What if remote sites holds better suited components with higher ranks than those already placed in the local repository? What policy to use in order to keep updating the local repository?
• The Crawling module searches for new components, do we need to insert an agent on every repository?
  
• How to manage the heterogeneous aspects between components? COM and CORBA components?
  
• Semantic web and ontology use might simplify the mapping and query even though it is considered to be a disadvantage for the designers of GRIDLE due to the unique usage of a unified taxonomy.
  

Link to the article
PS: According to the Ranking algorithm, the rank of the page hosting the article increased while the rank of my blog is decreasing, actually I am offering a portion of my page's rank.

Review: An IPv6-Based Identification Scheme

This article presents an IPv6 identification scheme to identify physical objects with
RFID tags. The identification is needed in different fields such as locating objects,
health care monitoring, military operations etc.

Their scheme is based on IPv6 unicast address:

010.Registry_ID[5].Provider_ID[16].0.8].Subscriber_ID[24].0[8].Subnet_ID[16].Interface[48].

(note that the "‘."’ is used as a concatenation operator and X[n] where n indicates the
number of bits used to code the field X).

Register_ID is allocated to organizations responsible for assigning network addresses.
Provider_ID is allocated to Internet service provider. 0[8] future extension.
To identify objects they propose to use the unassigned IPv6 namespace that has the
binary prefix "‘001"’ with two formats:

General ID:
0010.Agency_ID[5].Domain_name[48].0[7].Object_Class[16].Serial_Number[48].

Agency_ID is analogous to registry ID, the agency is responsible for allocating the
identifier. Domain name for company or organization. 0[7] future use. Object class to
identify object types. Serial number ID of an object type.

Pseudo Random ID:
0011.Agency_ID[5].Random_Number[119]

This scheme provides more privacy, it does not reveals the ID of the company and other information. They clearly distinguish between and IPv6 address to locate an object and IPv6 ID
to identify and object. The prefix translation is what they propose to translate between an IPv6 ID (prefix 001) and an IPv6 address prefix (010) which means that the IPv6 ID may be used to
obtain an IPv6 address. Since physical objects are mobile, they propose the following
two methods to track objects:

Name System: (Same ID, multiple addresses)
They propose to use canonical name written in a reverse order in which they are constructed.
They reverse it so it can be used as a URL DNS like. By doing this, they can integrate their scheme in existing systems like DNS.

Serial_number.object-class.company.organization.obj.
DNS query will start at "obj"’ level than it will go from right to left.

When objects moves, we need only to update DNS records which maps a name into an address. When objects moves to a different domain, the new owner of objects should update the DNS record. Since DNS is not suited for updates, a localization service provided by the proxy should handle the update.

Address forward scheme:
They use the home agent approach (see Mobile IP paragraph).
They assume that routers are configured to distinguish identifiers from addresses.
We can search for an object by its ID because routers will translate the IPv6 ID into an IPv6 address by modifying the 3 bits prefix. The ID will remain the same and so the address. Objects of the same owner are assigned to a dedicated proxy. The proxy’s address will have same domain prefix. When a router receives an object ID, it translates it and forwards it to the correspondent proxy according to the domain name. When an object moves, its ID and so its address remains the same. The object updates his home proxy with the new location where it moved recently. It also informs the new proxy about its ID. Routers will forward the packets to the proxy according to the domain name. This proxy will have the same role as a home agent in an IP mobile. The proxy will forward requests to the new proxy where the object has moved.

The approach is very comprehensive specially the mapping between ID and address with the 3 bits prefix and the facility of integration in today’s system without major modifications and without a need to query directories like DNS.
However since objects are usually manufactured in thousands and millions (Gillette raisers) when a container moves from an owner to another. The traffic update will generate a massive overhead between owners.
We are faced to the same problems when dealing with mobile IP. We lost object’s trace during transition from one proxy to another.
Not all companies have the same productions capacities. Small companies manufacturers small number of items which means that small companies will not use the IDs assigned to it, while big companies will exhaust ID in a short time (comparing to small companies). Should small companies share the domain ? This means that proxies of small companies cannot use a routing mask when dealing with IDs and IP addresses.
Two companies can share same domain, these 2 companies will have same prefix and since it cannot apply a mask. A proxy will list all the IDs of owned objects. Proxies will be overloaded then and I/O time query will be slow due to the huge amount of data.
Mobile IP approach what if home proxy or company owner of the domain is closed for economic or other reasons. How to maintain the address forwarding?

Link to the article

Review: BonAHA - Service Discovery Framework for Mobile Ad-Hoc Applications

This article proposes a framework for service discovery. It is based on the mutlicast DNS (used also by apple bonjour). BonAHA as its name indicates is used for Ad-Hoc applications. (Bonjour for Ad-Hoc Application).

Service discovery protocols in Ad-Hoc require the developer to add network monitoring, node arrival/departure in/from the network. Applications need to be aware of such changes in a such mobile and dynamic networks.
However Bonjour is not suitable for Ad-Hoc networks due to the absence of a state view of the network.
BonAHA uses a concept of service. Application can register/listen to a particular service on a network. Service names are DNS-like.
Services are discovered by instantiating a service object and registering it to respond to network events.

Applications announcing a service follows these steps:
* Create a service object with the name of the service
* Set any metadata associated to the object
* Register it

Applications listening to service announcements follows these steps:
* Create a service object with the name of the service
* Set an event handler object for this service
* The class handling events for the service will handle events corresponding to node updates.
* Metadata associated with that node can be retrieved from the nodes.

The BonAHA API has two classes and one interface:
Class Bservice: allows to construct a service instance.
Interface BListener: handles node entry/update and departure.
Class BNode: correspnd to a node in the network offering a service and exposes metadata such as host name, host address, service name etc.



This article proposes a framework for service discovery and an API to allow developers to concentrate on the application part without handling the topology modifications.
Some issues remains unclear:
Services are not published on a central node due to the Ad-Hoc characteristic.
A node will listen then to service announcements. This means that it is not aware of services currently available in the network because it arrived after the announcements.
When registering a new services, announcement is broadcasted over the whole network? This does not results a huge overhead for every service announcement.
Can we use DHT table approach to store metadata associated to services available on the network?
What is the cost for maintaining service's updates due to node arrival/departure?

Link to the article