Envisaged Publish-Subscribe Functionality

Having described the state of current solutions, we now illustrate what pub-sub functionalities we envisage in auctioning platforms. Afterwards, we outline the implications of these extensions for users and elaborate on their acceptance. Enhanced Publish-Subscribe Functionality

As previously mentioned, our goal when integrating pub-sub functionalities into online auctions is to supportively enrich the process of discovering items for potential buyers. We believe that this functionality is highly desirable for private users of online auctions as identified in Section 3.1.1, and it solves the problems discovered in Section 3.1.

We analyzed the existing schema for online book auctions on eBay, in particular for fiction book auctions. This schema allows for the specification of various attributes for book items. We give an overview of these attributes and their domains in Table 3.1. Column 1 shows the name of the attribute; its description and some example values are given in Column 2. The last column specifies the domain for possible attribute values. eBay allows users to specify some of these attributes when querying for items. However, they can only combine their specifications in a conjunctive way, not leaving room for non- trivial queries (see Section 3.1.1) and leading to the drawbacks identified in Section 2.6 (page 58).

When integrating pub-sub mechanisms into auctions, users should be able to restrict all of these attributes in a more flexible way. That is, they should be able to constrain them and to combine these constraints by Boolean operators. This approach allows, for example, the specification of different prices for new and used book copies. We give several examples of simple but non-conjunctive subscriptions in Section 3.3.

Evidently, this support for more complex subscriptions leads to questions regarding user acceptance and user satisfaction. We elaborate on these aspects in the next subsection. However, studying such implications in detail is beyond the scope of this dissertation. This work is left to researchers in the human- computer interaction area.

Acceptance of Enhanced Functionalities

If just searching for items using existing query functionalities, the available conjunctive semantics in current auctioning platforms might be sufficient. Al-

Table 3.1: Overview of attributes for book auctions on eBay. Attribute Description or example Domain or values Category Category of the book, e.g., Enumeration,

humor, poetry, fantasy 22 values Format Format of the book, e.g., Enumeration,

hardcover, softcover 4 values Special Attribute Special attribute of the book, Enumeration,

e.g., first edition, signed 3 values Condition Condition of the book, e.g., Enumeration,

New, used 2 values

PayPal Specifies whether seller accepts Boolean PayPal5_(yes/no)

Buy It Now Specifies whether the book is Boolean sold for a fixed price (yes/no)

Price Price of the book Number,

2 fractional digits Auction Title Title of the auction Free text

Title Title of the book Free text

Description Description of the book Free text Ending Within Ending time of the auction, Time,

e.g., 1 hour, 9 days up to 10 days

Language Language of the book, Enumeration,

e.g., English, French 14 values

Publication Year Year of publication Natural number, up to current year Quantity Number of books available Natural number,

greater than 1

Bids Number of bids Natural number,

greater than 0

5

though, these mechanisms are neither flexible nor general enough for pub-sub functionalities. The conjunctive operator might be the easiest operator to use [YS93], but in pub-sub systems users need to formulate more restrictive subscriptions. This is due to the need to achieve a higher precision6 _{in order to}

avoid annoying, unnecessary notifications. The traditional ranking approach (see, e.g., Maron and Kuhns [MK60]) is not applicable to pub-sub systems. The reason is that the relevance of an auction has to be determined without the knowledge of future items on offer (also previous, already-finished auctions do not necessarily help in determining a rank).

The appreciation of the requirement to formulate more restrictive and pre- cise subscriptions is directly fostered by the benefits for users: the need to fully exploit an existing subscription language will be realized at least in case of large numbers of false positives. Such experiences will lead to more skilled users with an awareness of accurately defined subscriptions. This includes the understanding of various Boolean operators in order to minimize the number of queries as well as the redundancies among queries. Users should thus be willing to invest more time for this definition of long standing subscriptions than for queries in the traditional search process. And these more experienced users are likely to formulate relatively compact Boolean queries [Ros04], that is, queries without strong redundancies.

Additionally, auctioning sites could apply graphical editors, for example, as proposed by Jones and colleagues [JMS99] or Jung [Jun07], to help users in the process of specifying Boolean queries. As already stated, an analysis of such means is out of the focus of this dissertation.

Having described the general application area of online auctions, we proceed with identifying typical event messages and the distributions for this scenario in the next section.