 Open Access
 Total Downloads : 25
 Authors : A.Monika, A.Niveda Rajlakshmi, M.Pavithra, Sk.Karthika
 Paper ID : IJERTCONV6IS07132
 Volume & Issue : ICONNECT – 2018 (Volume 6 – Issue 07)
 Published (First Online): 24042018
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Mining Frequent Itemset for Temporal Data using Hybrid Algorithm

onika CSE Department
TRP Engineering College Trichy,TamilNadu

iveda Rajlakshmi CSE Department TRPEngineering College Trichy,TamilNadu
M.Pavithra CSE Department
TRP Engineering College Trichy,TamilNadu
S K. Karthika Assistant Professor CSE Department TRP Engg College Trichy,TamilNadu
AbstractTemporal data are data with timestamping information.The result of data mining also depends on time stamp information.Traditional techniques assume that datasets are static and the rules being used are relevant for the entire dataset. In this paper, we are trying to improve the efciency of mining frequent itemsets on temporal data. To solve this problem we produce a list based data structure and pruning technique that allow to mine frequent itemset from a uncertain frequent pattern.
KeywordsUncertain Frequent Pattern,Temporal Data,Time Stamp,Itemsets
DATA MINING is the process of discovering interesting patterns and knowledge from voluminous amounts of data [1]. One of the most important applications of data mining is the analysis of transactional data. Databases which originate from transactions in a supermarket, bank, department stores and, etc., are all inherently related to time.These are called temporal databases which are databases that contain timestamping information [3].Capturing the cooccurrence of items in transactions was rst proposed by Agrawal et al. [2]. For example, given a transactional database of a supermarket, we may have {milk,bread} bought together with support of 20%. It means that 20% of all transactions contain milk and bread together..One important extension to frequent pattern mining is to include a temporal dimension [4]. For example, milk and bread may be ordered together in 80% of all transactions between 7 and 9A.M while their support in the whole database is 20%.Infact, interesting patterns are often related to the specic period of time; therefore, the time during which they can be observed is important.
ID ITEMS

bread,milk

milk,rusk

milk,biscuit
From the above,the conclusion is we can obtain different pattern for different time intervals. Discovering such patterns may lead to useful knowledge. The discovery of such association rules has been discussed in the literature. In this context, sequential association rules [5], time intervals for association rules [6], [7] and calendarbased association rules [4], [8] are some interesting studies in recent years.
In this paper, we conduct a study on developing an efcient algorithm for mining frequent patterns and their related time
interval from transactional database. Then a new algorithm is proposed based on two thresholds, support, and density as a novel threshold. Frequent itemsets are discovered and neighbouring time intervals are merged.
The rest of the paper is organized as follows. In Section II, we discuss some related work in comparison with our work. In Section III, the proposed algorithm is presented in details. The notion of TCs is described and the essence of a density threshold is illustrated with an example. In Section IV, we present the experimental evaluation of our algorithms using synthetic datasets and give analysis on experimental results. In Section V, we conclude the paper with some discussions

RELATED WORK

Association rule was rst proposed by [2]. It has two part, nding frequent itemsets and generating association rules. The major and time consuming part of the algorithm is discovering frequent itemsets and generating association rules is straightforward. Therefore, in our literature review, we consider association rules the same as frequent itemset mining. Classication association rule uses class tables and maximum support count which is efficient and eliminates infrequent item sets. But duplicate data elimination is difficult [9][11], contextbased association rule uses association rule and accuracy, frequency and performance is high but sequential and parallel construction of table is difficult due to time factor [12][14],negative association rule[15],fuzzy association rule [16], generalized association rule [17][19] are some of the research areas in this eld. Among these extensions, the time attribute of the transactions has attracted many researchers to discover frequent itemsets over time omputational time is low. The problem of discovering association rule that display regular cyclic variation overtime was rst proposed by Ozdenetal. [20]. Two new algorithms were presented, sequential algorithm and interleaved algorithm, to discover hourly, daily, weekly, etc., patterns. Some pruning techniques also used to improve the performance of the algorithms. It should be noted that by their method, each cyclic rule holds in every cycle with no exception. However, in real life, patterns are not perfect. Therefore, Han et al. [21] proposed partial periodic pattern mining in temporal database. Discovered association rules show behavior in some but not all points in time. The work of Ozdenetal in[20]was extended by Ramaswamy et al. in [22] to discover userdened temporal patterns in association rules. The idea of using calendar algebra was proposed to describe interesting patterns, however, it requires users prior knowledge to dene calendar
expressions.In[6],Ale and Rossi proposed the idea of extracting rules over a specic period of time that is shorter than the whole database.The lifetime of each item was used to dene time intervals. The concept of temporal support was introduced for the rst time and algorithm a priori was modied to incorporate time. Li et al. [4], [23] proposed an approach to discover association rule holds either in all or some time intervals. Instead of using cyclic [20] or usergiven calendar algebraic expressions [22], calendar schema is used to restrict the meaningful time intervals. Since items have different exhibition periods, algorithm progressivepartition miner (PPM) was proposed to discover patterns in such databases [24], [25]. The basic idea of PPM is to rst partition the database in light of exhibition periods of items and then progressively accumulate the occurrence count of each candidate 2itemset based on the intrinsic partitioning characteristics. Its worth noting that exhibition period of items in[24]and[25]is the same as lifetime of items in[6].The study of [24] and [25] was further extended [26], considering the importance of time intervals. Using the same concept proposed in [6] and [24], algorithm segmentedprogressive lter (SPF) was introduced in [27] to rst segment the database into sub databases in such a way that items in each sub database will have either starting time or ending time. Then, for each subdatabase, SPF progressively lters candidate 2itemsets with cumulative ltering thresholds either forward or backward in time. Lee and Lee [28] also used calendar algebra to discover association rules.Since human being tends to be uncertain,fuzzy set theory incorporated to help the construction of desired time intervals. This is similar to the work of Ramaswamy et al. [22], but it is more exible which is because of the fuzzy sets and fuzzy operators. Junheng[29]added some modication to the algorithm SPF
[27] to increase efciency. Results show that its performance outperform from prior methods. Huang et al. [30] explore the previous studies [27], [29] to remedy drawbacks of their algorithms. Algorithm TWAIN was presented to nd association rules that are absent when the whole rage of the database is evaluated altogether.Mahantaetal.[8]presented a method which is able to extract different types of periodic patterns that may exist in a temporal dataset.The user do not need to specify the periods in advance. Set operation called set superimposition was used for storing periods associated with itemsets. Adhikari et al. [31] enhanced the study of [8] by proposing a new data structure for storing and managing patterns. They also introduced minor changes to their algorithm to improve its performance. Lee et al. [32] proposed an efcient algorithm for discovering fuzzy periodic association rules. They investigated the problem of discovering regular time intervals, i.e., the periodicity. To overcome the difculties of nding precise time interval, fuzzy calendar was proposed. Their method scan the database at most twice for discovering association rules and related time periods. Matthews et al. [33] used genetic algorithm to nd temporal association rules for the rst time. Genetic algorithm was employed to simultaneously search the rule space and temporal space. They used the strength of evolutionary algorithms in searching for association rules and optimizing parameters of induction process (support and condence values). They further extended their works for nding fuzzytemporal association rules where Duplication can be minimised to very little amount and provides good response time [34], [35]. The problem of it is it doesnt handle very large number of data.
[37] proposed a new form of association rule, i.e., association rule with time windows. The main purpose of their study was to nd the time intervals for association rules which may be arbitrary in length and not user specied. They further optimized the process of nding time windows by mathematical modeling [7]. Saleh and Masseglia [38] deal with this problem from another viewpoint. The concept of solid itemset mining was proposed to nd the subsets of database that contain frequent itemsets and then the proposed algorithm was developed based on that .The problem is that Usage of tree structure and other nodes uses more memory.Like above studies, the challenge was to nd the optimal time interval.
Proposed Algorithm
We propose a Listbased UNcertain frequent pattern mining Algorithm (LUNA), which is an efficient and exact method for mining uncertain frequent patterns based on novel data structures and mining techniques that can guarantee the correctness of the mining results without any false positives. The main contributions of this paper are as follows:

Proposing a new paradigm for efficiently mining uncertain frequent patterns from uncertain databases.

Devising novel data structures based on list forms that can store uncertain data more efficiently compared to tree structures of previous approaches.

Proposing an algorithm that can extract exact results of uncertain pattern mining without any false positives using the suggested data structures.

Suggesting new prepruning techniques that can improve the mining performance of the proposed algorithm by preventing useless mining operations from being caused, and effective strategies that can speed up the mining operations without any additional memory consumption.
LUNA algorithm
In this section, we describe an overall procedure of LUNA, the proposed exact UFP mining algorithm that applies the suggested data structures and mining techniques as well as various performance improving techniques. Fig. 10 shows the overall pseudo code of the proposed algorithm. LUNA first scans a given uncertain database, D, and computes the expSup value for each item composing D (lines 0103). After that, the algorithm discards items with lower expSup values than a given minSup and calculates a support ascending order of the remaining items (lines 0405). Moreover, these items are extracted as 1length UFP s (line 06). After a series of initialization processes for UPList s are conducted (line 07), the second database scanning operations are performed to construct UPList s (lines 0810). In this process, tuple data and Max information for each UPList are updated according to the method mentioned in Section 3.4.1. Thereafter, the algorithm performs a series of works for constructing CUPList s from the generated UPList s (lines 1126). Once an UPList is selected (line 11), the algorithm initializes a set of CUPList s, C , and a prefix itemset, pref (line 12), and sets the item of the currently selected UPList to pref (line 13). Then, another UP List after the currently selected one is chosen again (line 14).
After calculating an overestimated expSup value from the selected two UPLists, the algorithm performs subsequent tasks for constructing a CUPList from them if the overestimated value is not smaller than minSup (lines 1521). In the middle of generating the CUPList, it can be possible to prune it according
to the proposed pruning techniques. The proposed algorithm improves its mining efficiency by utilizing the existential
probability information of the prefix. If expSup of the constructed CUPList is higher than or equal to minSup (line 17), the CUP List is stored into a set of CUPList s for the next mining task (line 18) and the pattern corresponding to the list is extracted as a valid UFP (line 19).
After a series of works for the UPList selected first, uk, are finished, if the number of CUPList s contained in C is higher than 1, subprocedure LUNA_growth is called to mine UFP s with longer lengths recursively. If the algorithm conducts the above operations with respect to all the UPList s, it can provide a complete set of UFPs from the given uncertain database.
The subprocedure, LUNA_growth, is recursively called to construct CUPList s and extract UFP s with 3 or longer lengths (lines 2843). The overall flow of this subprocedure is similar to the part between lines 11 and 26 in the main procedure. The major differences between them are that (1) the prefix information is continually updated to perform the mining operations more efficiently for each call of the subprocedure (line 30) and (2) CUP List s for longer patterns are recursively generated from previous CUPList s until there is no more CUPList to be combined (lines 3142).


Equations
1 (Expected Support of a Pattern (expSup)). Let X i1, i2, . . . , is be a pattern composed of items belonging to I. Then, the existential probability of X for each transaction Tx, p(X , Tx), is computed as follows.
p (X , Tx) =ik Tx
p(ik, Tx)

Figures and Tables
An example of uncertain datasets
A 
B 
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100 
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0.9 
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<> 
Algorithm 3.1: Algorithm for mining frequent itemsets with LUNA Algorithm
Fig. Story Board of the proposed algorithm.
Memory Usage(Accident)
Runtime results (Accidents).

COMPUTATIONAL STUDY
In this section, experimental study is carried out by applying the proposed algorithm. The performance of the algorithm is examined in the experiment on synthetic data. In the following, we describe the process of generating synthetic dataset.

Generation of Synthetic Data
A synthetic dataset is chosen rather than a real dataset so that a controlled experiment can be conducted to validate the efcacy of our approach. The IBM quest synthetic data generator [5] has been used to generate a dataset for experimentation. As the dataset is nontemporal, so it cannot be
used directly. We have incorporated the temporal feature in the dataset; so, it can be a temporal dataset and can be handled by our algorithm. We developed a program for this. The program takes starting date, ending date, and synthetic data as inputs and randomly distributes data between the starting and ending dates. Dataset features such as number of items, number of transactions, average transaction length, and time span of the dataset can be set by the user. As there is no guarantee that the generated dataset contains pattern withtemporal information, augmentation tothe original dataset is proposed. The augmented pattern act as a target, and the aim of our algorithm is to discover this target pattern. The augmentation method is now described. The a priorialgorithm is used to identify frequent patterns on original dataset. One of the patterns is selected and augmented in a new copy of the dataset. After selecting a pattern, augmentation occurs by inserting it as a transaction to the intended time interval with no additional items; so, no unexpected correlations between items are introduced. The result is a dataset that has an increase in the selected pattern in the intended time interval. The objective is to nd this pattern by our algorithm.

Experiment on Augmented Dataset
The dataset is a synthetic database containing transactions madeupby100itemsfrom01/01/2015 00:00:00to01/01/201600:00:00.Thenapatternischosenasatarget solution.Thegoal behind using such a large dataset for analysis is to make sure that our proposed algorithm is capable of handling any frequent itemset mining problem. Considering time hierarchies of the time stamp, i.e., month, day, hour, a specic time interval for augmenting a pattern is chosen. From a priori, itemset {61,70,91}is a frequent pattern. We assume that this pattern is frequentbetween7and9A.M.,1stand2nddaysoftherstthree months of 2015. This time interval contains 3Ã—2Ã—3 BTCs. For each BTC, 100 transactions are augmented which include only items 61, 70, and 91. Our algorithm should be able to nd this itemset and its temporal information. The proposed algorithm is coded by Java programming language and is run on a notebook computer using an Intel Core i7, 2.5 GHz CPU with
16 G of memory and running windows 10.Asweexpected,targetsolution,i.e.,pattern{61,70,91}was mined in the specied time interval at a reasonable time. Fig. 4 shows the relationship between the solution time and minimum supports at different densities. As we can see, the lower the minimum support, the higher the solution time is. It is also worth noting that with support level less than 20%, many other useful patterns is found in addition to the target solution. Although there is not a considerable differences between solution time with different density threshold, but nowwe guarantee thatdata patterns found are valid and no overestimating of the time periods has been occurred.
This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.
Fig. 4. Solution time of the proposed algorithm against different minimum supports (a) = 30%. (b) = 50%.

Experiment on Real Dataset
As the density threshold is proposed in this study and is dened for the proposed algorithm, we could not compare the
results of our method with others. But instead, we use a real dataset of a grocery store to compare the results of this section with Section IVB. The dataset is available from website at http://mi.ua.ac.be/data/. We use the same procedure which is proposed in Section IVA to change the nontemporal dataset to temporal one. The total number of items is 331 and total number of transactions is 9835. We run the program with minimum support 50% and equal to 20%. Total of 88 patterns wasfoundbyouralgorithmin1222seconds (20.3minutes).As we can see, runtime of the algorithm heavily depends on minimum support threshold and number of items. Increasing in the number of items and transactions, adds more complexity to the problem and though runtime of the algorithm increases. As we can see in Table III, soda, bottled water, and whole milk weres old together during specict ime interval.Therefore, many marketing strategies can be applied to increase the prot of the store.For example,according to the crossselling strategy, items with less interest from the customers perspective can be placed between frequent patterns in specic time intervals to increase the selling rate.

Analysis of Scalability
In this section, for analyzing the scalability and fair comparison of the performance of the algorithm, several experiments are carried out and then we compare the results of our algorithm with [8]. Several experiments are designed and in each experiment, the objective is to nd a target solution in an augmented dataset. The obtained results from numerous runs of the algorithm with different number of items and transactions at different periods of time is shown in Table IV. In all of the experiments, the minimum support is 25% and density rate is 50%. Also the augmented target is the same for all experiments. We can see how the proposed algorithm perform well in almost all of the experiments. By comparing experiments 1 and 2, we can infer that solution time increases when number of items and average transaction length increase which is reasonable.Comparing experiments3and4 and also5 and 6,it is seen that solution time increases, when the time period is increased. This seems logical since increasing the time interval, increases the solution space. We also compare the results of our algorithm with the work of[8].They considered a small dataset consisting of timestamp and items sold at the corresponding dates which is collected over two months, i.e., January 2000February 2000. The total number of items is 5, total number of transactions is 60. The dataset is given in Table V. In order to compare the results, we use the same minimum support, i.e., 50%, and run the program. The runtime of our algorithm is 0.079 seconds and results are shown in Table VI. In terms of the number of detected patterns, the number of patterns detected by [8] is less than ours. In terms of the quality of the detected patterns, the results show that some of the patterns extracted by [8] are not valid. For example, [8] stated that itemset {1,2} is frequent in period [12] [49]. However, the results of our algorithm indicate that this itemset is frequent in Time stamps Items Time stamps Items Time stamps Items the period [49] in the rst month, and in the period [310] in the second month. Even with more accurate survey of dataset, it is clear that the tiny time frame in which itemset {1,2} become frequent is [58] and not [49]. Our proposed algorithm is able to detect this defect and has extracted more accurate patterns.


CONCLUSION
In this paper,we studied the mining of frequent itemsets along with their temporal patterns.Some patterns are held during some time intervals while others may happen periodically. The main feature of our proposed algorithm is that a new notion of TCs is presented to consider time hierrchies in data mining process. It enables us to nd different kinds of temporal patterns. for small or mediumsized datasets, it can nd the solution in less than one minute. we applied our algorithm to market basket dataset with time stamps. from managerial viewpoint, results of our algorithm can help managers to make better decisions.duplicate data are eliminated easily.it is easier to implement in large database.performance is high compared to original apriori
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