One of the best presentations that I have seen lately is Mark Little talking about REST and WS at QCon London 2008, or rather about the differences between the uniform interfaces and the specific interface. Mark Little gets right at the bottom of the differences between REST and WS, and these differences are not all differences between architectural styles, but rather differences in organizations.

One of the best interpretations of the differences in REST vs WS that I have seen is the one that Mark makes in this presentation and that I will try to reproduce below is the division of tasks of mapping a message sent to an entity (could be a service, could be an URL) and the component/processor within that entity that will process it: when you send a message to a specific interface you will be specifying the method and the component that will process that message, so the message-to-processor mapping is done by the client. Whereas when you send a message to a specific interface you need to attach some meta-data to that message which will be used by the entity implementing the specific interface for mapping that message to its appropriate processor, therefore the message-to-processor mapping is done by the entity.

The message-to-processor mapping is externalized in the case of specific interfaces while the uniform interface internalizes it. These different mappings come with different transaction costs: in the case of the external mapping the costs are synchronizing the client with changes in the specific interface while in the case of the internal mapping the costs are adapting the uniform interface’s mapper to changes in the meta-data (a new type of messages should be mapped to a new processor).
Now, if we apply economics to the task of message-to-processor mapping we would start to get some interesting results. According to Coase’s theorem you can externalize an activity if the transaction costs for that carrying that activity are low enough and if the transaction costs are high then that activity is better internalized. It would follow that when the transaction costs of this mapping are low you can externalize it via a specific interface, otherwise you would be better off to internalize it via an uniform interface. 
The transaction costs of the specific interface are the synchronization of distributed clients and this could be resolved either thru versioning, or by not modifying the specific interface or by standards. If you can keep these costs down it follows that you can delegate the message-to-processor mapping efficiently to the client else you are better off with a uniform interface. Keeping these costs down also implies that the number of methods that get exposed is kept down in order to avoid the number of changes (more methods, more opportunities for changing them). Generally speaking interaction via specific interfaces is best limited to a few coarse-grained components, between a few participants and with components which do not change very often.
The above synchronization costs run counter to scale in number of clients: as the number of clients starts to grow you are starting to have problems synchronizing all of them and eventually the transaction costs of using the specific interface will become so high, it will not make sense to use it. One corollary of this is that the uniform interface is far better at the scale of the internet and this is probably the main reason why it is used at this scale.
The above will provide a pretty good guide to an architect trying to figure out whether to use a specific interface or an uniform one because their use is not driven by technology, but rather by the organization(s) within which they are employed.

Another interesting point in his presentation was the effort for creating a REST-ful standard for carrying out distributed transactions and the need for agreement between multiple parties. As I was saying in a previous post about REST and WS the differences between these 2 camps are more of organizational nature than anything else. Mark touched upon the fact that even if the need for carrying out distributed transactions via REST exists there is still no standard for doing so, that the REST community seems pretty much happy with implementing low-level infrastructure and not with higher-level, and higher-value, components. I find this a pity and I have the impression that this need will be fulfilled only it raises to a level at which major corporations will find profitable for getting involved. The REST community appears simply way too fragmented to be able to carry out this effort on its own…

Anyway, go ahead and watch the presentation, it is the most thoughtful presentation on distributed computing that I have seen in a while.

ESBs is an essential enterprise computing capability which allows for mediating connections between various parties. Typical EBS usage consists of message producers sending messages to an ESB which transforms them and then forwards them to message consumers.

It is at the transformation stage that the thorniest issues arise with ESBs. As outlined in this presentation from Thoughworks there is a tendency to push business logic inside the ESB resulting in a very tight coupling between applications and the ESB (part of the business logic will be stored in applications, part of it in the ESB and the business logic in the ESB will need to be kept in sync with the business logic in the applications). Not a nice scenario and unfortunately the solution provided in the presentation (apparently you only need to use Guerilla SOA) doesn’t say much. The business logic which gets shoved into the ESB in the above example are the relationships between the various parties which are sending each other messages and the mess that comes out of it as these relationships change over time.

One example of ESB usage is a customer-facing web application which takes purchase orders from customers and sends messages to an inventory and shipping system, to the accounts receivables system and to the customer loyalty system. There are a few ways that this messages can be sent: 1) the web-application sends only one message to the ESB which then creates 3 more messages, one for the inventory system, one for the accounting system and one for the customer loyalty system (in which case the relationships between the web-app and the 3 systems are managed within the ESB); 2) the web-application creates 3 messages which are all sent independently to the 3 systems (in which case the relationship between the web-application and these 3 systems is managed by the web-app typically thru dedicated senders which are transforming the message according to the other party’s specs) or 3) the web-app publishes the message on the ESB which forwards it as-is to the receiving systems which are receiving the message as it has been created by the web-app and transform it according to their rules (in which case the receiving systems are managing the relationships with the web-application typically thru dedicated receiving points which are transforming the incoming messages).
So far I have only seen 2 or 3 used and it was used successfully. I have not seen 1 being used successfully, but rather I have seen ESBs simply delegated to the role of a dumb-pipe while the processing is done on the end-points. I think that the main reason for which the ESB cannot grow beyond the role of a dumb-pipe is that the transformations typically involve data, imagine that in the above scenario the IDs of the products on the web-application are different from the ones in the inventory system (a very common case BTW). In order to service this transformation you would need an up-to-date mapping between all relationships that it is managing. Sooner or later that ESB will turn into a giant vacuum cleaner that will need to suck every byte of data available in order to service the relationships stored in it.
Lesson #1: Managing relationships typically involves managing data.

Let’s go more into the gory details and think about how we would deal with stale data: let’s say that the datastore holding the mappings of product IDs from the webapp to the inventory systems is missing a product ID (another very common case). In the case where the relationships are maintained at the connection end-points (message producers or consumers) the operation team managing those end-points would have access to the exception (missing product ID mapping in this case) as well as to its solutions (create this mapping in your mapping store). How will the ESB deal with stale data? Well, the ESB will have to find the entity which can resolve this exception, package the exception and send it to that entity. Sooner or later the ESB gets becomes a spaghetti bowl.
Lesson #2: ESB has bad exception management capabilities. 

Pushing the transformation towards the end-points effectively couples the end-points because these endpoints must share the format (*) of the messages they exchange and, just as importantly, they need to share data. Sharing data is usually done by one party having a procedure to export its data and the other parties using this procedure for creating local replicas of that data and synch-ing them according to a calendar. In addition to that the parties replicating the data have procedure for overriding the data they receive and adding to it. As far as I have seen it works pretty well and when it doesn\t work it is more of a management issue on the side issuing the data.

To sum this up, I would keep any data enriching out of the ESB and use the ESB trasformations only for format transformations and version transformations (**). One more benefit to keeping the ESB down to routing and format transformations would be that its role is well-contained and it doesn’t turn into a wild-card (does this particular problem gets handled by the ESB, how, why, when, etc…) making your IT assets more manageable. This results in a neater division of concerns in your overall enterprise architecture.

* It is advised that the format of these messages is not using APIs but rather text-based protocols such as XML, pipe-delimited, etc… API couplings is one of the most horrendous things that I have seen, synch-ing libraries on multiple endpoints at the same time is an incredibly time-consuming activity.

** Version-based transformation are transformations of the same message between 2 different versions of it: let’s say that one message producer decides to publish a new version of the messages that it has been produced so far, the ESB should be made aware of this and deliver the new version to the consumers that are registered to receive it as well as create a new message with the old version out of the original message and send this new message (formatted according to the old version) to the clients which are still registered to receive the old version. Part of this versioning effort is the transformation from the current version to an older version and this transformation would be best done by the message producer which will load a transformer into the ESB for this transformation. The ESB will then be re-configured to apply this transformation to the original message with the new version and the resulting message to be routed on its old route. This way the versioning effort will be pushed inside the ESB and messages will be delivered transparently to the intended receipients and recipients will not have to be upgraded when their counterparties upgrade their message format effectively de-coupling their release cycles.

Urmaresc de o buna bucata de vreme criza financiara care bantuie pietele financiare de mai bine de un an de zile, iar in ultima vreme o urmaresc chiar foarte atent citind vreo duzina de analize zilnic. Nu vreau sa-mi arog vreo autoritate in materie, citesc mai mult pentru ca sunt foarte interesat de finante si pentru ca este de departe cel mai important eveniment din ultima vreme.

Tot citind asa m-am intrebat ce se scrie oare in Romania, mai mult pentru a vedea daca mai am mare lucru in comun cu cei de acolo. Eram curios in primul si in primul rand sa vad cum se pune problema in Romania in privinta unui lucru care pentru mine conteaza destul de mult. Eram de asemenea curios sa vad cam ce fel informatii i se paseaza unui roman de rand pentru ca el sa-si faca o idee despre acest fenomen. Am inceput cu unul din ziarele pentru care aveam un oarecare respect: Cotidianul.

Cotidianul mi se pare (de la 7 fuse orare distanta) un ziar al carui audienta este constituita din clasa de mijloc a Romaniei, audienta cu care reusesc sa ma identific cel mai mult: oameni cu anumite studii, care se bucura de un anumit succes si care au opinii liberale in sensul europeean al cuvantului. Primul articol despre sub-prime pe care l-am vazut a fost acest editorial scris de nimeni altul decat de Mircea Dinescu. Mda, marele poet s-a trezit peste noapte economist si a inceput sa-si dea cu parerea despre interventia statului in economie. Dupa inca un editorial al lui Dinescu mi-a fost clar ca mai bine ar fi ramas la o betie cu Marx, macar asa cititorii ar fi fost mai castigati.
Bun, pe Dinescu l-am bifat, hai sa vedem ce mai e in Cotidianul despre criza financiara. Pai, ce sa fie, articole pe un subiect economic scrise de tot felul de tipi care n-au mare lucru in comun cu finantele si economie: Teodor Baconski (aparent de profesie teolog) ne explica diferentele dintre pietele de capital din Statele Unite si cele din Europa, Alin Fumurescu (politolog  se pare) ne explica de ce politica este superioara economiei si cum ar fi fost evitat acest fenomen daca politicienii ar fi fost bagati pe fir, etc…

In fata acestei incropeli de opinii am decis ca vreau sa vad si alte pareri din alte ziare. Si asa am ajuns la Romania Libera si la editorialul Alina Mungiu-Pippidi (de profesie politolog). Spre deosebire de confratii de mai sus ai dansei care se multumeau sa formuleze diverse opinii despre economie doamna Pippidi ridica stacheta: este primul intelectual care are curajul sa scrie o opinie asupra planului Paulson (nota: planul Paulson este un plan destul de complex care nu se poate rezuma in cele 2 fraze pe care i le consacra Alina Mungiu-Pippidi). Singurul lucru care merita citita in acest articol este prima fraza: Daca ar fi sa sintetizez actuala criza globala financiara pe intelesul meu, as face-o cam asa. Odata ce ne previne ca dansa nu intelege mare lucru Alina Mungiu-Pippidi incepe sa bata campii. Odata cu acest editorial mi s-a taiat pofta sa mai citesc ce scris Romania Libera despre criza financiara.

Apoi am luat o mica pauza de la sub-prime pentru ca am inceput ca citesc ce scrie Evenimentul Zilei despre sub-prime. EZ nu scrie nimic, dar chiar nimic, intre meciul vietii, analiza EZ si dezastru in fotbal n-am gasit mai nimic despre actuala criza financiara. EZ a fost ultimul cotidian ne-specializat pe care m-am uitat, chiar n-aveam chef sa-mi pierd toata ziua citind ziare din Romania.

Asa ca hai sa trecem la niste ziare specializate. Am inceput cu ziarul Bursa, primul ziar financiar din Romania si pe care mi-l aminteam dinainte sa fi plecat (m-am dus pe situl lor mai mult dintr-o nostalgie pentru logo-ul lor neschimbat de mai bine de 15 ani). Am zburat de pe situl lor in mai putin de 30 de secunde, asta dupa ce am facut cunostinta cu calendarul Bursei. Am crezut initial ca o sa am de a face cu ceva asemanator cu calendarul Barrons in care redactorii fac un rezumat al principalelor evenimente din saptamana care urmeaza. Ei bine, Bursa are un calendar diferit , este vorba de un calendar de agata in perete, nu va recomand sa apasati pe el la locul de munca, veti da peste o tipa sumar imbracata intr-o pozitie provocatoare.

OK, deci asta a fost Bursa. Ia sa vedem Ziarul Financiar. ZF este intr-o liga diferita de Bursa, in primul rand pentru ca nu are calendar ci o gramada de reclame care-ti ingreuneaza cititul. ZF are chiar si o rubrica in care sunt colectate diferitele articole referitoare la criza financiara curenta. Destul de interesant materialul in acesta rubrica, din pacate ii cam lipsesc editorialele. Eu de fapt asta cautam, cautam o serie de articole in ziarele din Romania in care romanului obisnuit sa i se explice cam ce se intampla, care sunt cauzele. Cautand in rubrica de mai sus niste explicatii am dat asupra 2 articole: un articol care expune parerile profesorilor din ASE si un articol care expune parerea lui Ion Iliescu (??????).
Parerile profesorilor din ASE par sa fie un amestec exotic de vechituri, misticism si ecologism:
“Bate la usa o noua viziune mondiala care va porni de la ideea ca FMI, Banca Mondiala trebuie respiritualizate (presupun ca conceptul de re-spiritualizare a unei banci este folosit in circuit inchis in ASE, eu inca n-am gasit ceva asemanator in proza economica anglo-saxona)”

De remarcat o diferenta importanta intre economistii de la ASE si economistii din Occident: economistii de la ASE nu cunosc cauzele acestei crize dar cunosc urmarile ei, in timp ce economistii din Occident cunosc foarte bine cauzele crizei, dar habar n-au ce se va intampla:
“Crizele acestea au cauze profunde, stiinta veche, clasica nu mai poate sa explice aceste evenimente. Va fi o respiritualizare a stiintei economice, cred ca noua stiinta economica se va numi ‘ecolonomie’, stiinta economica despre sanatatea intregului viu.“ 

Un ultim citat din articolul de mai sus care ar trebui sa ne arate cu cine stam de vorba:
Din punct de vedere tehnic, nu este nicio diferenta intre pierderea a 70 sau a 700 de miliarde de unitati monetare intr-o singura zi. 

Dupa elucubratiile de mai sus suntem adusi rapid pe pamant de limba de lemn a lui Ion Iliescu:
Dincoace, este vorba de cealaltă extremă: a fetişizării pieţei şi a capacităţilor ei, adică este vorba despre un neoliberalism care spune: “statul out (a se remarca folosirea romglezei, semn ca Iliescu e in pas cu trendu-ul), iar economia se reglează de către piaţă şi regulile ei”. Aceasta este iarăşi o extremă care se dovedeşte, iată nerealistă. Adevărul este undeva, la mijloc. 

Ultimul articol din ZF pe care l-am citit este acesta in care America este comparata cu un Bancorex (voi reveni la paralelele dintre crash-urile financiare de la noi si cele din Statele Unit). Nici aici nu sunt prezentate informatii despre cauzele actualei crize economice, potentialele canale de contagiune, etc… ci un mic tratat ieftin despre venalitatea oamenilor.

As mai fi urmarit si alte surse de informatii economice din Romania dar intre timp ma cam saturasem. Dupa un scurt sejur pe Lumea In Criza unde cel mai interesant articol este o traducere proasta din engleza am pus punct.
Dupa cum va spuneam mai sus as fi vrut sa stiu cam ce parere poate sa-si faca un roman obisnuit care citeste ziarele din Romania si am ajuns la opinia ca nu poate sa-si formeze nici o opinie, ci este inundat de stiri din care nu intelege mare lucru si care-l lasa intr-o stare avansata de panica.

Daca as fi sa rezum impresiile cu care am ramas dupa ce am facut aceasta mica revista a presei romanesti as scrie asa ceva:

• Lucrul care m-a socat cel mai tare este lipsa de discernamant cu care diferite personalitati publice (Alina Mungiu-Pippidi, Mircea Dinescu, etc…)  s-au oferit sa-si dea cu parerea despre lucruri despre care habar n-au. Eu ma simt putin tras in piept de amatorismul acestor intelectuali in care la un moment dat chiar credeam destul de mult. Opiniile pe care le-au dat cu aceasta ocazie ma fac sa ma intreb cand vorbesc despre un domeniu pe care-l cunosc bine si cand alearga dupa cai verzi pe pereti. Sincer sa fiu eu unul voi fi extrem de circumspect cand voi mai citi ceva scris de ei.
• Lipsa de personalitati in domeniul finantelor sau al economiei. Elitele Romaniei nu au un Martin Wolf, Willem Buiter, Paul Krugman si canalele aferente prin care acesti oameni sa poata intra in comunicare cu romanul obisnuit care ar dori sa stie mai multe lucruri despre acest fenomen foarte important pentru zilele noastre.
• Amatorismul presei financiare din Romania care se pare ca nu e in stare de a prezenta analize mai adanci asupra acestei crize si care se limiteaza la difuzarea de stiri non-stop catre o audienta care pare incapabila sa le inteleaga. Audienta nu e capabila sa le inteleaga si pentru ca presa financiara nu este in stare sa o educe.
• Am ramas de asemenea si cu impresia ca multi compara actuala criza cu crahurile bancare de la noi si ca in acest act introduc o doza masiva si iresponsabila de “sa moara si capra vecinului”. Dragii mei, va rog sa luati in calcul ca daca moare capra asta voi o sa zburati din functiile in care sunteti mai repede decat poti sa zici sub-prime. Dupa cum seful Reservelor Federal Americane spunea, s-ar putea ca maine sa nu mai existe o economie.
• Exista un interes destul de mare pentru ceea ce se intampla afara.

Aici inchei acest post. Presupun ca daca cineva va poposi aici va ajunge printr-un search Google si ca va cauta informatii despre actuala criza economica. Pun aici o lista de diferite articole care il pot lamuri. Singura problema este insusirea unui anumit vocabular, articolele sunt pline de termeni tehnici cu care majoritatea oamenilor s-ar putea sa aiba probleme. Daca cineva are dificultati in intelegerea termenilor il rog sa puna intrebari in comentarii si voi incerca sa-i raspund daca voi avea timp.

Deci aceasta este lista:

• Paul Krugman despre planul de salvare. Ce mi se pare cel mai important in acest articol este cum PK rezuma istoria actualei crize in 4 fraze, mai putin analiza planului.
• Problemele actuale ale firmelor de investitii rezumate de Richard Balwin. Problemele reducerii de capital prin investitii in ipoteci sub-prime si diferentele dintre problema de lichiditate (o institutie financiara are banii bagati in active solide, dar nu-i poate scoate din aceste active fara a le pune pe piata in cantitati masive, lucrul care ar face ca pretul activelor, si implicit valoarea institutiei, sa scada) si insolvabilitate (institutia financiara are banii bagati in active “toxice”). De asemenea discuta problemele de leverage si de-leverage dezordonat.
• Diferitele mecanisme prin care criza financiara din Statele Unite poate atinge Europa.
• O anatomie a crizei financiare de pe vox. Vox este un alt site pe care sunt publicate diferite analize despre aceasta criza.
• Blogul lui Willem Buiter - destul de complex, cere o intelegere destul de buna a diferitelor instrumente financiare.
• Free Exchange - un bun blog de popularizare a diferitelor concepte economice, in momentul de fata are o masa rotunda axata pe actuala criza financiara.
• The Euro-Intelligence blog. Personal, consider acest sit destul de alarmist. Totusi, daca faci abstractie de acest lucru poti gasi informatii destul de utile si link-uri catre alte sit-uri la fel de utile, mai ales despre situatia din Europa.
• Martin Wolf’s Forum.