First compensation-based solution is shown in Figure 1. Here, VM (View Maintenance), VS (View Synchronization) and VA (View Adaptation) are general view algorithms based on different types of source updates [12,13,14]. To solve the concurrency problems, we propose to apply local-compensation algorithm in the "Query Engine" to handle concurrent data updates and concurrent rename schema changes. To resolve the concurrency caused by concurrent drop schema changes , we introduce a new algorithm called "Dyno" to dynamically schedule the maintenance order of the updates to solve the conflicts. The details could be found in [5].

Second multiversion-based solution is shown in Figure 2. Here, A new transaction model (DWMS_Transaction) is introduced which integrates both base update transaction and maintenance transactions. We then rephase the DW maintenance anomaly problems to the serializability of the DWMS_Transactions. To achieve such serializability, we introduce a multiversion algorithm for concurrency handling, in particular, the versioned data are stored in the "TxnWrap" [3]. We also explore several optimizations based on this approach, such as wrapper optimization, parallel DW maintenance, batch DW maintenance etc [1,4].