on 18-Sep-2018 (Tue)

A decentralised database with minimal trust between nodes would al- low for the creation of a global ledger. Such a ledger would have many useful applications in finance, trade, supply chain tracking and more. We present Corda, a decentralised global database, and describe in detail how it achieves the goal of providing a platform for decentralised app develop- ment. We elaborate on the high level description provided in the paper Corda: An introduction 1 and provide a detailed technical discussion

1 Introduction

In many industries significant effort is needed to keep organisation specific databases in sync with each other. In the financial sector the effort of keeping different databases synchronised, reconciling them to ensure they actually are synchronised and resolving the ‘breaks’ that occur when they are not represents a significant fraction of the total work a bank actually does! Why not just use a shared relational database? This would certainly solve a lot of problems using only existing technology, but it would also raise more questions than answers:

• Who would run this database? Where would we find a sufficient supply of angels to own it?
• In which countries would it be hosted? What would stop that country abusing the mountain of sensitive information it would have?
• What if it were hacked?
• Can you actually scale a relational database to fit the entire financial system?
• What happens if The Financial System™ needs to go down for mainte- nance? • What kind of nightmarish IT bureaucracy would guard changes to the database schemas?
• How would you manage access control

• Nodes are arranged in an authenticated peer to peer network. All com- munication is direct.
• There is no block chain 3 . Transaction races are deconflicted using plug- gable notaries. A single Corda network may contain multiple notaries that provide their guarantees using a variety of different algorithms. Thus Corda is not tied to any particular consensus algorithm. (§7)
• Data is shared on a need-to-know basis. Nodes provide the dependency graph of a transaction they are sending to another node on demand, but there is no global broadcast of all transactions.
• Bytecode-to-bytecode transpilation is used to allow complex, multi-step transaction building protocols called flows to be modelled as blocking code. The code is transformed into an asynchronous state machine, with checkpoints written to the node’s backing database when messages are sent and received. A node may potentially have millions of flows active at once and they may last days, across node restarts and even upgrades. Flows expose progress information to node administrators and users and may interact with people as well as other nodes. A Flow library is provided to enable developers to re-use common Flow types such as notarisation, membership broadcast and so on.

3 The peer to peer network
3.1 Network overview
A
Corda network consists of the following components:

• Nodes, communicating using AMQP/1.0 over TLS. Nodes use a relational database for data storage.
• A permissioning service that automates the process of provisioning TLS certificates.
• A network map service that publishes information about nodes on the network.
• One or more notary services. A notary may itself be distributed over multiple nodes.
• Zero or more oracle services. An oracle is a well known service that signs transactions if they state a fact and that fact is considered to be true.

They may also optionally also provide the facts. This is how the ledger can be connected to the real world, despite being fully deterministic. A purely in-memory implementation of the messaging subsystem is provided which can inject simulated latency between nodes and visualise communica- tions between them. This can be useful for debugging, testing and educational purposes. Oracles and notaries are covered in later sections.

3.2 Identity and the permissioning service

Unlike Bitcoin and Ethereum, Corda is designed for semi-private networks in which admission requires obtaining an identity signed by a root authority. This assumption is pervasive – the flow API provides messaging in terms of identities, with routing and delivery to underlying nodes being handled automatically. There is no global broadcast at any point. This ‘identity’ does not have to be a legal or true identity. In the same way that an email address is a globally unique pseudonym that is ultimately rooted by the top of the DNS hierarchy, so too can a Corda network work with arbitrary self-selected usernames. The permissioning service can implement any policy it likes as long as the identities it signs are globally unique. Thus an entirely anonymous Corda network is possible if a suitable IP obfuscation system like Tor 6 is also used.

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The dubious notion that philosophy is a guide to calmer living is as old as the field itself. Saint Augustine described philosophy as a “harbor” for troubled souls in a fourth-century monograph on the happy life, and the sixth-century Roman senator Boethius titled the treatise he wrote while awaiting execution “The Consolation of Philosophy.” More recently, in his Philosophical Investigations (1953), Ludwig Wittgenstein suggested that the aim of philosophy is not to seek the truth but rather to provide relief—“to show the fly the way out of the fly-bottle.” Wittgenstein didn’t embrace “a single philosophical method.” Instead he concluded, “There are indeed methods, different therapies” to quiet the buzz of our puzzlement.

HIKING WITH NIETZSCHE: ON BECOMING WHO YOU ARE

BY JOHN KAAG

Farrar, Straus and Giroux

Nietzsche, by contrast, had no stomach for palliatives. As John Kaag reflects in his new memoir cum philosophical excursion, Hiking With Nietzsche: On Becoming Who You Are, the German thinker aimed “to terrify rather than instruct us.” “Become who you are,” the quotation that Nietzsche chose for the epigraph of his graduate dissertation, is a line from the Pythian odes of the Greek poet Pindar. Bereft of context, this pronouncement can sound as flabbily vacant as the text of a self-help manual. After all, how could anyone fail to become who she is? Is there any instruction more trivial? The full Pindar quote, however, outlines a daunting assignment: “Learn and become who you are.” Nietzsche knew that if philosophy can serve as therapy, it’s by delivering an electric jolt to the soul.

This article appears in the October 2018 issue.

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The dubious notion that philosophy is a guide to calmer living is as old as the field itself. Saint Augustine described philosophy as a “harbor” for troubled souls in a fourth-century monograph on the happy life, and the sixth-century Roman senator Boethius titled the treatise he wrote while awaiting execution “The Consolation of Philosophy.” More recently, in his Philosophical Investigations (1953), Ludwig Wittgenstein suggested that the aim of philosophy is not to seek the truth but rather to provide relief—“to show the fly the way out of the fly-bottle.” Wittgenstein didn’t embrace “a single philosophical method.” Instead he concluded, “There are indeed methods, different therapies” to quiet the buzz of our puzzlement.

“Learn and become who you are.” Nietzsche knew that if philosophy can serve as therapy, it’s by delivering an electric jolt to the soul.

Kaag, the philosophy-department chair at the University of Massachusetts at Lowell, began experimenting with what might be called first-person philosophy—not desiccated fodder for arcane journals but robust inquiry into what he calls the “stuff of everyday life”—in his 2016 book, American Philosophy: A Love Story

Mingling romance and scholarship, Kaag related how he stumbled onto the private library of a 20th-century philosophical eminence, then out of a miserable marriage and into the arms of his now-wife, the Kantian philosopher Carol Hay. As Kaag and Hay worked to preserve the library’s holdings, they didn’t find consolation, exactly. Instead, they grappled with transcendentalists like Ralph Waldo Emerson and pragmatists like William James. Along the way, they came to regard love as a challenge rather than a balm. In Hiking With Nietzsche, Kaag describes the draw of Nietzsche’s marital ideal—a union that embodies “the will of two to create the one that is more than those who created it,” never lapsing into “one long stupidity.”

Kaag is fascinated by the idea of decadence—which Nietzsche first broached in The Birth of Tragedy, and which would preoccupy him for the rest of his life: “Is it perhaps possible to suffer from over-abundance?” he asked. “Is there perhaps such a thing as neuroses of health?” Blending biography, intellectual history, and personal essay, Kaag follows three related journeys: Nietzsche’s evolution from adolescent upstart to middle-aged iconoclast, Kaag’s youthful attempt to retrace Nietzsche’s footsteps through the Swiss Alps, and Kaag’s adult effort to retrace his own retracing, this time with Hay and their 3-year-old daughter in tow. The result is not just an approachable introduction to Nietzsche’s thought. Kaag’s book is also, despite its cloying title, a confirmation that philosophy thrives when it provides an antidote to the wholesome doldrums of sanity.

Nietzsche’s academic career was marked by a number of dazzlingly early successes. At 24, he was the youngest tenured faculty member at the University of Basel. But by 28, he had been demoted from wunderkind to pariah, thanks in large part to the publication of his first book, The Birth of Tragedy (1872). More a work of creative interpretation than a piece of faithful exegesis, the debut departed sharply from accepted philological method, infuriating Nietzsche’s colleagues. It argued that two aesthetic tendencies vied for dominance in ancient Greece: the Dionysian, a primordial blurring of the borders dividing self and world, and the Apollonian, a rationalist paradigm that positioned art as an ordered alternative to the havoc of life. Though Nietzsche regarded these two forces as mutually enhancing—and he lauded tragedy for wedding them—his real allegiance lay with the Dionysian, as his life and work went on to attest.

At 19, Kaag shared Nietzsche’s distaste for the “scripted” routines and glib gratifications that make modern life so deplorably easy. When he arrived in Basel on a research trip, he recoiled at his surroundings: The train station was “a model of Swiss precision,” and the streets were “too straight, too quiet, too mundane.” He quickly abandoned his plans to ruminate on Nietzsche from the confines of Basel’s library and instead decided to follow his idol’s grueling alpine route to “Splügen, then to Grindelwald at the foot of the Eiger, then to the San Bernardino Pass, to Sils-Maria, and finally to the towns of Northern Italy.” He wanted, he writes, “to feel something, to break through the anesthesia, to prove to myself that I wasn’t just asleep

When he heads back to his family after a day of lonely hiking, he reflects, “Perhaps a pilgrim triumphs not in hardship, but in the rare moment when they learn to accept something soft at home.” This sounds like an un-Nietzschean lesson, and Kaag’s clichés can sometimes leave us wondering whether he embraces Wittgenstein’s vision of philosophy after all.

But to Kaag’s credit, he is determined to inject hints of extremity into his outwardly stable life. By the time he returns to America, he has modified his conception of how, exactly, we should go about steeling ourselves in the face of the decadent imperatives of a consumerist, conformist world. What Kaag overlooked in his youth is that Nietzsche does not prescribe difficulty for its own sake. Though the metaphorical language Nietzsche employed throughout his career is wildly inconsistent, he was ultimately an advocate of health—but health, he emphasized, is not synonymous with enjoyment. On the contrary, health requires the trials that beget a strong constitution

Kaag needed two trips to the Alps to grasp that Nietzsche counsels us to celebrate our suffering because we can avoid it only if we avoid engagement—only if we insulate ourselves from the hardship that is part and parcel of even the most placid human existence. Kaag concludes that a celebration of life needn’t entail self-immolation, but it necessarily entails difficulty. “The self does not lie passively in wait for us to discover it. Selfhood is made in the active, ongoing process, in the German verb werden, ‘to become,’ ” he writes.

Life goes on for Kaag, of course, and the threat of complacency looms: “Syllabi were dutifully written. Conferences were studiously organized. Bathrooms were meticulously cleaned.” But Kaag resists—not by fasting or hiking mountains in inadequate footwear but by recalling as often as possible, in the intervals between deadening and dulling, that “things must suffer, go dark, perish before they live again. This is not an escape or respite from life but rather its realization.” Kaag may have outgrown his youthful dramatics, but he continues to let philosophy upend him. It once took him all the way to the edge of an Alpine precipice, to the brink of starvation. It went on to undo one marriage and inspire another. And it continues to heal us, not by making us feel better, but by making us well.

The difference between define an object and build an object: Define an object: a geometric object in Salome is defined only the six basic geometric objects Building an object: a geometric object in Salome can be built by objects other than the basic ones Example: the cube Define: eight vertex , twelve edge , etc. Build: two vertex in the global coordinate system (parallel to global axis)

A wire is not necessarily plane.

A wire is collection of several edge

A face is not necessarily plane

A shell is collection of several face

We can define as many local coordinate system objects as necessary. In particular, a local coordinate system object allows you to define the workplane of the 2D sketch utility. Remarque: The global coordinate system is created by default. If you accidentally destroy it, you can re-draw it using the New entity Basic Origin and Base Vectors command.

To construct shell with hole(s), use face with hole(s)

A line object is a special edge object because it is straight whereas a edge object can be curved (see objects circle , ellipse , and arc )

o build circle : New entity Basic Circle The circle object will create a curved edge object that closes on itself. So it has only one object vertex (but which is not the center!)

The Bezier curve ( ): is a edge curved object defined by its control points (Beziers polynomials). The set constitutes a (single) object edge curve (which can constitute an open or closed curve). This object contains two vertex objects and one edge object for the open case and one vertex object for the closed case. It can also be defined by a parametric parametric equation with three parameters. Since this curve is not interpolating, it does not pass through all vertex objects but only by the first and the last

extruding a wire will create an object of type shell extruding a face will create an object of type solid

n Salome, an object block is a geometric entity that will allow to mesh with rectangles or hexahedrons.