The sharing of caches among Web proxies is an important technique to reduce Web traffic and alleviate network bottlenecks. Nevertheless it is not widely deployed due to the overhead of existing protocols. In this paper we demonstrate the benefits of cache sharing, measure the overhead of the existing protocols, and propose a new protocol called "summary cache". In this new protocol, each proxy keeps a summary of the cache directory of each participating proxy, and checks these summaries for potential hits before sending any queries. Two factors contribute to our protocol's low overhead: the summaries are updated only periodically, and the directory representations are very economical, as low as 8 bits per entry. Using trace-driven simulations and a prototype implementation, we show that, compared to existing protocols such as the Internet cache protocol (ICP), summary cache reduces the number of intercache protocol messages by a factor of 25 to 60, reduces the bandwidth consumption by over 50%, eliminates 30% to 95% of the protocol CPU overhead, all while maintaining almost the same cache hit ratios as ICP. Hence summary cache scales to a large number of proxies. (This paper is a revision of Fan et al. 1998; we add more data and analysis in this version.).

Summary cache: a scalable wide-area web cache sharing protocol

The Visual Display of Quantitative Information

In this paper we review the literature relating to the psychological/educational study of programming. We identify general trends comparing novice and expert programmers, programming knowledge and strategies, program generation and comprehension, and object-oriented versus procedural programming. (We do not cover research relating specifically to other programming styles.) The main focus of the review is on novice programming and topics relating to novice teaching and learning. Various problems experienced by novices are identified, including issues relating to basic program design, to algorithmic complexity in certain language features, to the “fragility” of novice knowledge, and so on. We summarise this material and suggest some practical implications for teachers. We suggest that a key issue that emerges is the distinction between effective and ineffective novices. What characterises effective novices? Is it possible to identify the specific deficits of ineffective novices and help them to become effec...

/pdf/learning-and-teaching-programming-a-review-and-discussion-2x8svsn4u8.pdf

Learning and Teaching Programming: A Review and Discussion

Operators of online social networks are increasingly sharing potentially sensitive information about users and their relationships with advertisers, application developers, and data-mining researchers. Privacy is typically protected by anonymization, i.e., removing names, addresses, etc.We present a framework for analyzing privacy and anonymity in social networks and develop a new re-identification algorithm targeting anonymized social-network graphs. To demonstrate its effectiveness on real-world networks, we show that a third of the users who can be verified to have accounts on both Twitter, a popular microblogging service, and Flickr, an online photo-sharing site, can be re-identified in the anonymous Twitter graph with only a 12% error rate.Our de-anonymization algorithm is based purely on the network topology, does not require creation of a large number of dummy "sybil" nodes, is robust to noise and all existing defenses, and works even when the overlap between the target network and the adversary's auxiliary information is small.

/pdf/de-anonymizing-social-networks-33ryd91uii.pdf

De-anonymizing Social Networks

http://rboutaba.cs.uwaterloo.ca/Papers/Journals/2010/Mosharaf10.pdf

A survey of network virtualization

For purposes of this paper, we define "Personally identifiable information" (PII) as information which can be used to distinguish or trace an individual's identity either alone or when combined with other information that is linkable to a specific individual. The popularity of Online Social Networks (OSN) has accelerated the appearance of vast amounts of personal information on the Internet. Our research shows that it is possible for third-parties to link PII, which is leaked via OSNs, with user actions both within OSN sites and else-where on non-OSN sites. We refer to this ability to link PII and combine it with other information as "leakage". We have identified multiple ways by which such leakage occurs and discuss measures to prevent it.

/pdf/on-the-leakage-of-personally-identifiable-information-via-3b7f6nyuyj.pdf

On the leakage of personally identifiable information via online social networks

Content distribution networks (CDNs) are a mechanism to deliver content to end users on behalf of origin Web sites. Content distribution offloads work from origin servers by serving some or all of the contents of Web pages. We found an order of magnitude increase in the number and percentage of popular origin sites using CDNs between November 1999 and December 2000.In this paper we discuss how CDNs are commonly used on the Web and define a methodology to study how well they perform. A performance study was conducted over a period of months on a set of CDN companies employing the techniques of DNS redirection and URL rewriting to balance load among their servers. Some CDNs generally provide better results than others when we examine results from a set of clients. The performance of one CDN company clearly improved between the two testing periods in our study due to a dramatic increase in the number of distinct servers employed in its network. More generally, the results indicate that use of a DNS lookup in the critical path of a resource retrieval does not generally result in better server choices being made relative to client response time in either average or worst case situations.

/pdf/on-the-use-and-performance-of-content-distribution-networks-v6lg57nayz.pdf

On the use and performance of content distribution networks

Online social networks (OSNs) with half a billion users have dramatically raised concerns on privacy leakage. Users, often willingly, share personal identifying information about themselves, but do not have a clear idea of who accesses their private information or what portion of it really needs to be accessed. In this study we examine popular OSNs from a viewpoint of characterizing potential privacy leakage. Our study identifies what bits of information are currently being shared, how widely, and what users can do to prevent such sharing. We also examine the role of third-party sites that track OSN users and compare with privacy leakage on popular traditional Web sites. Our long term goal is to identify the narrow set of private information that users really need to share to accomplish specific interactions on OSNs.

/pdf/characterizing-privacy-in-online-social-networks-52fhpjdn7u.pdf

Characterizing privacy in online social networks

For the last few years we have been studying the diffusion of private information for users as they visit various Web sites triggering data gathering aggregation by third parties. This paper reports on our longitudinal study consisting of multiple snapshots of our examination of such diffusion over four years. We examine the various technical ways by which third-party aggregators acquire data and the depth of user-related information acquired. We study techniques for protecting privacy diffusion as well as limitations of such techniques. We introduce the concept of secondary privacy damage. Our results show increasing aggregation of user-related data by a steadily decreasing number of entities. A handful of companies are able to track users' movement across almost all of the popular Web sites. Virtually all the protection techniques have significant limitations highlighting the seriousness of the problem and the need for alternate solutions.

/pdf/privacy-diffusion-on-the-web-a-longitudinal-perspective-2x503qd9ak.pdf

Privacy diffusion on the web: a longitudinal perspective

For purposes of this paper, we define "Personally identifiable information" (PII) as information which can be used to distinguish or trace an individual's identity either alone or when combined with other information that is linkable to a specific individual. The popularity of Online Social Networks (OSN) has accelerated the appearance of vast amounts of personal information on the Internet. Our research shows that it is possible for third-parties to link PII, which is leaked via OSNs, with user actions both within OSN sites and elsewhere on non-OSN sites. We refer to this ability to link PII and combine it with other information as "leakage". We have identified multiple ways by which such leakage occurs and discuss measures to prevent it.

Craig E. Wills

Papers

On the leakage of personally identifiable information via online social networks

On the use and performance of content distribution networks

Characterizing privacy in online social networks

Privacy diffusion on the web: a longitudinal perspective

On the leakage of personally identifiable information via online social networks